Hello,
There has been a while since you've posted this thread. Have you find a workaround?
I have to say: Please search first in SCN. Since the issue you met has been discussed a lot in SCN. There will be big chance a thread which shows you didn't make thorough search in SCN will be rejected. 
For your case, please check
http://scn.sap.com/thread/1864300
which mentioned that the error is because webgui/ITS does not support office integration.
Thus I assume that for your case, it will be reproducible without CRM web ui. That is if you test directly with webgui ITS URL, the same error will be there.
If you diidn't find a workaround, I'd like to suggest to use transaction launcher launched using SAP GUI for your Z program, which can bypass this issue.
Hongyan