CreateESRISpatialReferenceFromPRJ returns The input is not a workstation prj

Hi,

Im getting the following error while trying to execute CreateESRISpatialReferenceFromPRJ(string prjString).
But when im using CreateESRISpatialReferenceFromPRJFile(string prjFile) with the same prj string in the file it works fine.

What does this exception means;
"the input is not a workstation prj"

Thanks,
Tom