"Standard Error ... 5 ... Value cannot be null. Parameter name: assemblyString" when use "Reports - Run" with DB2 database

Symptom

Screen
Information
Standard Error
Number: 5
Source: FrangoDirect.ExcelLinkD.FetchValues#ControllerProxyClient
Description: Ssytem.Web.Services.Protocols.SoapException: Server was unable to process request. ---> System.ArgumentNullException: Value cannot be null.
Parameter name: assemblyString
at
Cognos.Controller.Proxy.CCRWS.ExcelLinkB_FetchValues(String....
<...>
[OK}

Event Viewer (Application Log) on Windows 2008 64-bit using Office 2007:

Log Name: Application
Source: Cognos Controller
Date: 22/06/2011 12:57:11
Event ID: 0
Task Category: None
Level: Warning
Keywords: Classic
User: N/A
Computer: SERVERNAME
Description:
Standard Error
Number: 5
Source: FrangoDirect.ExcelLinkD.FetchValues#ControllerProxyClient
Description: System.Web.Services.Protocols.SoapException: Server was unable to process request. ---> System.ArgumentNullException: Value cannot be null.
Parameter name: assemblyString
at Cognos.Controller.Proxy.CCRWS.ExcelLinkB_FetchValues(String sGuid, DataSet rsKeys, String sMcurr, Boolean bLocLang, String sUser, String sRep, Boolean bIsLnk, String sSortOrd, Int32 lOptBitSet)

Event Viewer (Application Log) on Windows 2003 32-bit using Office 2003:

Event Type: Warning
Event Source: Cognos Controller
Event Category: None
Event ID: 0
Date: 22/06/2011
Time: 13:12:31
User: N/A
Computer: SERVERNAME
Description:
Standard Error
Number: 5
Source: FrangoDirect.ExcelLinkD.FetchValues#ControllerProxyClient
Description: System.Web.Services.Protocols.SoapException: Server was unable to process request. ---> System.ArgumentNullException: Value cannot be null.
Parameter name: assemblyString
at Cognos.Controller.Proxy.CCRWS.ExcelLinkB_FetchValues(String sGuid, DataSet rsKeys, String sMcurr, Boolean bLocLang, String sUser, String sRep, Boolean bIsLnk, String sSortOrd, Int32 lOptBitSet)
--- End of inner exception stack trace ---
at Microsoft.VisualBasic.ErrObject.Raise(Int32 Number, Object Source, Object Description, Object HelpFile, Object HelpContext)
at Cognos.Controller.Common.RaiseErrCli.RaiseError(Int32 lErrNo, String sErrSource, String sErrDesc, String sErrHelpFile, Int32 lErrHelpContext)
at Cognos.Controller.Direct.ExcelLinkD.FetchValues(DataSet rsKeys, String sMcurr, Boolean bLocLang, String sRep, Boolean bIsLnk, String sSortOrd, Int32 lOptBitSet)
at Cognos.Controller.Reports.ExcelLink.RunReportEx()

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