Further to my original post the error has occurred several more times but I have found details of the error in the server event log as follows - the problem appears to be that when the user types in something invalid (location in the example below) navision should just give an error message to the user and allow them to continue but in some cases it is closing the users connection and reporting the error in the event log:
Service: MicrosoftDynamicsNavServer$LiveSvr01
User: SPALDINGS\ST Anderson
Type: Microsoft.Dynamics.Nav.Types.Exceptions.NavFatalCSideException
Message: Your connection to the server was closed due to the following problem. Location Code ‘5’ does not exist. [83951621]
StackTrace:
at Microsoft.Dynamics.Nav.Runtime.NavRuntimeAdapter.ErrorHandler(Int32 errorCode, Int32 errorNumber, Int32 moduleNumber, String errorText)
at Microsoft.Dynamics.Nav.Runtime.NativeMethods.AdapterValidateFieldNoFlowValidation(IntPtr connectionHandle, UInt32[] serverIndirectPermissions, IntPtr tableHandle, IntPtr recHandle, Int32 fieldNo, Boolean isUserInput)
at Microsoft.Dynamics.Nav.Runtime.NavRecord.ValidateField(NavFieldEvent fieldEvent, NCLMetaField metaField, Boolean isUserInput)
at Microsoft.Dynamics.Nav.Runtime.NavRecord.Validate(NCLMetaField metaField, NavValue newValue, NavRecord callerRecord, Boolean isUserInput)
at Microsoft.Dynamics.Nav.Runtime.NavRecord.ValidateUserInput(Int32 fieldNo, NavValue newValue, NavRecord callerRecord)
at Microsoft.Dynamics.Nav.Service.NsDataAccess.Validate(Int32 fieldId)
at Microsoft.Dynamics.Nav.Service.NSField.ValidateField(NavConnection connection)
at Microsoft.Dynamics.Nav.Service.NSField.Validate(NavConnection connection)
at Microsoft.Dynamics.Nav.Service.NSService.<>c__DisplayClass36.b__35(Connection connection)
at Microsoft.Dynamics.Nav.Service.NSService.ExecuteOperation[T](String operationName, ServiceOperation`1 operation, Connection connection, Boolean revertLanguageChanges, WindowsIdentity impersonationIdentity)
Source: Microsoft.Dynamics.Nav.Ncl
Type: Microsoft.Dynamics.Nav.Types.Exceptions.NavCSideException
ErrorCode: 83951621
ErrorNumber: 5
ModuleNumber: 1
SuppressMessage: False
FatalityScope: None
Message: Location Code ‘5’ does not exist.