Web user interface doesn't start - Server error message

After installing and starting the service, I cannot get the web user interface to work.

Browsing to the location in the link hidden in the Event Broker directory, I get:

Server Error in '/' Application.

Runtime Error
Description: An application error occurred on the server. The current custom error settings for this application prevent the details of the application error from being viewed.

The following appears in the event log:

Event Type: Warning
Event Source: ASP.NET 4.0.30319.0
Event Category: Web Event
Event ID: 1310
Date: 22/04/2011
Time: 5:43:52 AM
User: N/A
Computer: IDB3TESTSDAY
Description:
Event code: 3008
Event message: A configuration error has occurred.
Event time: 22/04/2011 5:43:52 AM
Event time (UTC): 21/04/2011 7:43:52 PM
Event ID: c1773dd94a354fcaafdb09a6ea6ae76e
Event sequence: 1
Event occurrence: 1
Event detail code: 0

Application information:
Application domain: 74b7d320-1-129478886307141250
Trust level: Full
Application Virtual Path: /
Application Path: C:\Program Files\UNIFY Solutions\Event Broker\Web\
Machine name: IDB3TESTSDAY

Process information:
Process ID: 4544
Process name: Unify.Service.Event.exe
Account name: NT AUTHORITY\SYSTEM

Exception information:
Exception type: ConfigurationErrorsException
Exception message: Could not load file or assembly 'System.Web.Helpers, Version=1.0.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35' or one of its dependencies. The system cannot find the file specified. (C:\Program Files\UNIFY Solutions\Event Broker\Web\web.config line 18)
at System.Web.Configuration.CompilationSection.LoadAssemblyHelper(String assemblyName, Boolean starDirective)
at System.Web.Configuration.CompilationSection.LoadAssembly(AssemblyInfo ai)
at System.Web.Compilation.BuildManager.GetReferencedAssemblies(CompilationSection compConfig)
at System.Web.Compilation.BuildManager.GetPreStartInitMethodsFromReferencedAssemblies()
at System.Web.Compilation.BuildManager.CallPreStartInitMethods()
at System.Web.Hosting.HostingEnvironment.Initialize(ApplicationManager appManager, IApplicationHost appHost, IConfigMapPathFactory configMapPathFactory, HostingEnvironmentParameters hostingParameters, PolicyLevel policyLevel, Exception appDomainCreationException)

Could not load file or assembly 'System.Web.Helpers, Version=1.0.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35' or one of its dependencies. The system cannot find the file specified.
at System.Reflection.RuntimeAssembly._nLoad(AssemblyName fileName, String codeBase, Evidence assemblySecurity, RuntimeAssembly locationHint, StackCrawlMark& stackMark, Boolean throwOnFileNotFound, Boolean forIntrospection, Boolean suppressSecurityChecks)
at System.Reflection.RuntimeAssembly.nLoad(AssemblyName fileName, String codeBase, Evidence assemblySecurity, RuntimeAssembly locationHint, StackCrawlMark& stackMark, Boolean throwOnFileNotFound, Boolean forIntrospection, Boolean suppressSecurityChecks)
at System.Reflection.RuntimeAssembly.InternalLoadAssemblyName(AssemblyName assemblyRef, Evidence assemblySecurity, StackCrawlMark& stackMark, Boolean forIntrospection, Boolean suppressSecurityChecks)
at System.Reflection.RuntimeAssembly.InternalLoad(String assemblyString, Evidence assemblySecurity, StackCrawlMark& stackMark, Boolean forIntrospection)
at System.Reflection.Assembly.Load(String assemblyString)
at System.Web.Configuration.CompilationSection.LoadAssemblyHelper(String assemblyName, Boolean starDirective)

Request information:
Request URL: http://localhost:8080/
Request path: /
User host address: 127.0.0.1
User:
Is authenticated: False
Authentication Type:
Thread account name: NT AUTHORITY\SYSTEM

Thread information:
Thread ID: 7
Thread account name: NT AUTHORITY\SYSTEM
Is impersonating: False
Stack trace: at System.Web.Configuration.CompilationSection.LoadAssemblyHelper(String assemblyName, Boolean starDirective)
at System.Web.Configuration.CompilationSection.LoadAssembly(AssemblyInfo ai)
at System.Web.Compilation.BuildManager.GetReferencedAssemblies(CompilationSection compConfig)
at System.Web.Compilation.BuildManager.GetPreStartInitMethodsFromReferencedAssemblies()
at System.Web.Compilation.BuildManager.CallPreStartInitMethods()
at System.Web.Hosting.HostingEnvironment.Initialize(ApplicationManager appManager, IApplicationHost appHost, IConfigMapPathFactory configMapPathFactory, HostingEnvironmentParameters hostingParameters, PolicyLevel policyLevel, Exception appDomainCreationException)

Custom event details:

For more information, see Help and Support Center at http://go.microsoft.com/fwlink/events.asp.