EntitySchemaValidationException: C could not be parsed into a valid DN

I've created an AD connector to manage AD groups. The groups can export fine from Broker, including members. However when attempting to import the groups again from AD, I get the following error:

Change detection engine import all items failed.
Change detection engine import all items for connector AD Groups failed with reason One or more errors occurred.. Duration: 00:00:00.1718731
Error details:
System.AggregateException: One or more errors occurred. ---> Unify.Product.IdentityBroker.EntitySchemaValidationException: C could not be parsed into a valid DN. ---> System.ArgumentException: String C is not of a proper distinguished name component format. Ensure characters are correctly escaped, and that the format is correct.
 at Unify.Framework.IO.DistinguishedNameComponent.CreateDNComponent(String dnComponentString)
 at Unify.Framework.IO.DistinguishedNameConversionFromString.CreateDistinguishedName()
 at Unify.Product.IdentityBroker.EntityDistinguishedNameTypeSchemaValidator.CreateValue(Object dataValue)
 --- End of inner exception stack trace ---
 at Unify.Product.IdentityBroker.EntityDistinguishedNameTypeSchemaValidator.CreateValue(Object dataValue)
 at Unify.Product.IdentityBroker.EntityMultiValueValidatorFactoryBase`3.<>c__DisplayClass1_0.<GetValidator>b__0(Object value)
 at System.Linq.Enumerable.WhereSelectEnumerableIterator`2.MoveNext()
 at System.Collections.Generic.List`1..ctor(IEnumerable`1 collection)
 at System.Linq.Enumerable.ToList[TSource](IEnumerable`1 source)
 at Unify.Product.IdentityBroker.EntityMultiValueObjectTypeSchemaValidator`3.CreateValue(Object dataValue)
 at Unify.Connectors.AD.LDAPValueTypeOperations.AddValueToEntity(IConnectorEntity connectorEntity, IEntitySchemaFieldDefinition valueType, DirectoryAttribute attribute)
 at Unify.Connectors.AD.ADConnector.TransformEntry(ADAgent agent, SearchResultEntry searchResultEntry, Int64& uSNChangedToken)
 at System.Linq.Enumerable.WhereSelectEnumerableIterator`2.MoveNext()
 at Unify.Framework.Collections.EnumerableExtensions.<ActionOnLast>d__10`1.MoveNext()
 at System.Linq.Buffer`1..ctor(IEnumerable`1 source)
 at System.Linq.Enumerable.ToArray[TSource](IEnumerable`1 source)
 at Unify.Product.IdentityBroker.AuditReadingAsyncConnectorDecorator.<>c__DisplayClass1_0.<GetAllEntitiesAsync>b__0(IEnumerable`1 entities)
 at Unify.Framework.Auditing.AuditingExtensions.<>c__DisplayClass7_0`1.<CreateAndSendLogEntryAsync>b__0(Task`1 t)
 at Unify.Framework.Auditing.AuditingExtensions.<>c__DisplayClass5_0`1.<TaskContinueWithExceptionPassthough>b__0(Task`1 t)
 at System.Threading.Tasks.ContinuationResultTaskFromResultTask`2.InnerInvoke()
 at System.Threading.Tasks.Task.Execute()
--- End of stack trace from previous location where exception was thrown ---
 at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)
 at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
 at Unify.Product.IdentityBroker.EventNotifierReadingAsyncConnectorDecoratorBase`1.<GetAllEntitiesAsync>d__1.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
 at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)
 at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
 at Unify.Product.IdentityBroker.ChangeDetectionImportAllAsyncJob.<ImportAllChangeProcess>d__6.MoveNext()
 --- End of inner exception stack trace ---
 at System.Threading.Tasks.Task.ThrowIfExceptional(Boolean includeTaskCanceledExceptions)
 at System.Threading.Tasks.Task.Wait(Int32 millisecondsTimeout, CancellationToken cancellationToken)
 at Unify.Product.IdentityBroker.ChangeDetectionImportAllAsyncJob.RunBase()
 at Unify.Framework.DefinedScopeJobAuditTrailJobDecorator.Run()
 at Unify.Product.IdentityBroker.ConnectorJobExecutor.<>c__DisplayClass30_0.<Run>b__0()
 at Unify.Framework.AsynchronousJobExecutor.PerformJobCallback(Object state)
---> (Inner Exception #0) Unify.Product.IdentityBroker.EntitySchemaValidationException: C could not be parsed into a valid DN. ---> System.ArgumentException: String C is not of a proper distinguished name component format. Ensure characters are correctly escaped, and that the format is correct.
 at Unify.Framework.IO.DistinguishedNameComponent.CreateDNComponent(String dnComponentString)
 at Unify.Framework.IO.DistinguishedNameConversionFromString.CreateDistinguishedName()
 at Unify.Product.IdentityBroker.EntityDistinguishedNameTypeSchemaValidator.CreateValue(Object dataValue)
 --- End of inner exception stack trace ---
 at Unify.Product.IdentityBroker.EntityDistinguishedNameTypeSchemaValidator.CreateValue(Object dataValue)
 at Unify.Product.IdentityBroker.EntityMultiValueValidatorFactoryBase`3.<>c__DisplayClass1_0.<GetValidator>b__0(Object value)
 at System.Linq.Enumerable.WhereSelectEnumerableIterator`2.MoveNext()
 at System.Collections.Generic.List`1..ctor(IEnumerable`1 collection)
 at System.Linq.Enumerable.ToList[TSource](IEnumerable`1 source)
 at Unify.Product.IdentityBroker.EntityMultiValueObjectTypeSchemaValidator`3.CreateValue(Object dataValue)
 at Unify.Connectors.AD.LDAPValueTypeOperations.AddValueToEntity(IConnectorEntity connectorEntity, IEntitySchemaFieldDefinition valueType, DirectoryAttribute attribute)
 at Unify.Connectors.AD.ADConnector.TransformEntry(ADAgent agent, SearchResultEntry searchResultEntry, Int64& uSNChangedToken)
 at System.Linq.Enumerable.WhereSelectEnumerableIterator`2.MoveNext()
 at Unify.Framework.Collections.EnumerableExtensions.<ActionOnLast>d__10`1.MoveNext()
 at System.Linq.Buffer`1..ctor(IEnumerable`1 source)
 at System.Linq.Enumerable.ToArray[TSource](IEnumerable`1 source)
 at Unify.Product.IdentityBroker.AuditReadingAsyncConnectorDecorator.<>c__DisplayClass1_0.<GetAllEntitiesAsync>b__0(IEnumerable`1 entities)
 at Unify.Framework.Auditing.AuditingExtensions.<>c__DisplayClass7_0`1.<CreateAndSendLogEntryAsync>b__0(Task`1 t)
 at Unify.Framework.Auditing.AuditingExtensions.<>c__DisplayClass5_0`1.<TaskContinueWithExceptionPassthough>b__0(Task`1 t)
 at System.Threading.Tasks.ContinuationResultTaskFromResultTask`2.InnerInvoke()
 at System.Threading.Tasks.Task.Execute()
--- End of stack trace from previous location where exception was thrown ---
 at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)
 at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
 at Unify.Product.IdentityBroker.EventNotifierReadingAsyncConnectorDecoratorBase`1.<GetAllEntitiesAsync>d__1.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
 at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)
 at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
 at Unify.Product.IdentityBroker.ChangeDetectionImportAllAsyncJob.<ImportAllChangeProcess>d__6.MoveNext()<---

The only multi valued field is the members field.