If your on a version of TestPartner that contains TSystemInfo and your getting that error message you may want to call CPWR support. I spoke with someone else who was having a similar issue with the Items property and it looked like some type of strange redefinition problem. Instead of getting an uppercase i for (I)tems they were seeing lower case. No matter how hard I looked, I couldn't find anywhere it may have caused the problem.
This is all of course, assuming, that you are using a correct property or method of the object.