Excel Web Part - Can't access excel on a different farm.

Hi,

I have two SP2010 farms that have Excel services enabled and configured.  Using Excel Webpart, I get the following error when trying to display an excel file located on the 2nd SP farm:

 The file that you selected could not be found. Check the spelling of the file name and verify that the location is correct.

The user does have the proper access on both farms.  I can display the same file if it is on the same far.  So it seem you can't use the Excel webpart to display file from a different farm?  Thanks