If you have Vista as a development machine, you should upgrade to SP2 or upload fixes described in the following knowledgebase article. Apparently, there is a difference in version of .NET Framework which prevents Script task from working properly.
http://support.microsoft.com/default.aspx?scid=kb;en-us;931846
This problem may occur also if you have .NET Framework 2.0 hotfix later than build 2.0.50727.300 installed.
