Timesheet Add Lines error

[John Smith]

I've got one project on a Project Server 2007 system that I can't add lines
to a timesheet for. Onscreen I get a "An unexpected error has occurred."
However, the following three lines are written to the log file:

03/09/2007 16:10:33.71 w3wp.exe (0x1254)
0x14B8 Project Server Project Server - General
0 Exception Exception occurred in method TimeSheet.PrepareTimesheetLine
System.ArgumentException: These columns don't currently have unique values.
at System.Data.ConstraintCollection.AddUniqueConstraint(UniqueConstraint
constraint) at System.Data.ConstraintCollection.Add(Constraint
constraint, Boolean addUniqueWhenAddingForeign) at
System.Data.DataTable.set_PrimaryKey(DataColumn[] value) at
Microsoft.Office.Project.Server.DataAccessLayer.Generated.TimesheetDalBase.ReadCustomFieldByProjUID(Guid
resUID, Guid projUID, Guid periodUID) at
Microsoft.Office.Project.Server.BusinessLayer.TimeSheet.PreloadActualsAndCustomFields(TimesheetDataSet
dsTS, Guid projectUID, DataSet dsPeriod, Dictionary`2 assignment2tlMap)
at
Microsoft.Office.Project.Server.BusinessLayer.TimeSheet.PrepareTimesh...04858c3d-a3ff-4e50-9ec4-86df3c683e0603/09/2007 16:10:33.71* w3wp.exe (0x1254)
0x14B8 Project Server Project Server - General
0 Exception ...eetLine(Guid tsUID, TimesheetDataSet& dsDelta, Guid[]
tlsNeedFill) at
Microsoft.Office.Project.Server.WebService.TimeSheet.PrepareTimesheetLine(Guid
tsUID, TimesheetDataSet& dsDelta, Guid[]
tlsNeedFill) 04858c3d-a3ff-4e50-9ec4-86df3c683e06

03/09/2007 16:10:33.85 w3wp.exe (0x0824)
0x0A30 Project Server Project Server - General
8mqg Exception System.Web.Services.Protocols.SoapException:
System.Web.Services.Protocols.SoapException: ProjectServerError(s)
LastError=GeneralUnhandledException Instructions: Pass this into
PSClientError constructor to access all error information at
Microsoft.Office.Project.Server.WebService.TimeSheet.PrepareTimesheetLine(Guid
tsUID, TimesheetDataSet& dsDelta, Guid[] tlsNeedFill) at
System.Web.Services.Protocols.SoapHttpClientProtocol.ReadResponse(SoapClientMessage
message, WebResponse response, Stream responseStream, Boolean asyncCall)
at System.Web.Services.Protocols.SoapHttpClientProtocol.Invoke(String
methodName, Object[] parameters) at
Microsoft.Office.Project.Server.WebServiceProxy.PSIProxyBase.InvokePSI(String
serviceName, String methodName, Object[] parameters)Any help would be appreciated.