same GruntHTTP.exe, different error.

[IMnewer]

GruntHTTP
Net40
useSSL

It can run in Win7 x64, but failed in Server 2012 R2:

Illegal characters in path.
at System.Security.Permissions.FileIOPermission.EmulateFileIOPermissionChecks(String fullPath)
at System.Security.Permissions.FileIOPermission.QuickDemand(FileIOPermissionAccess access, String fullPath, Boolean checkForDuplicates, Boolean needFullPath)
at System.Net.WebClient.GetUri(String path)
at System.Net.WebClient.UploadString(String address, String data)
at GruntStager.GruntStager.ExecuteStager()

Why?