When I combine pdf document “A” (10 pages) with pdf document “B” (50 pages) I get 1 of 2 warnings: either “expected a string object” or “bad parameters.” The resulting document “C” is (in this example) 59 pages with page 1 of document “B” missing.
This suggests that your file "B" is corrupt, and more specifically, that the corruption is on the first page. There is not much you can do to fix this problem. If you created this document, and you still have the original file you used to create the PDF, I would re-create the document and see if that fixes the problem. If it does not, then chances are that something you've included on that page is causing this problem (could be e.g. a corrupt image, or a corrupt font).