[Adding pages to existing pdf causes error 1073741827]

taking an existing pdf file with FusionPro fields working fine, but when I add a page and try to compose it says:

 

CachePDF; error 1073741827: Bad parameter.

Graphic is not found or is not processed properly: /Users/imac/Desktop/myjob/file.pdf: Page 3

Check for file existence and that it is of the proper format.

 

any reason i shouldn't be able to modify the pdf after adding variable data fields to it?

 

thanks