Conversion of 89 MB files to word fails continuous, but 22 MB files succeeds. Why?

I can convert 22 MB pdf files to Word without problems, but conversion of 89 MB pdf-files with same origin (ie NOT scanned) continue failing. The error message is “Conversion failed” when trying by the Web Browser method and “An error occurred when trying to access the service” when converting directly from Adobe Reader.The file size does not exceed Adobes limit 100 MB, so what is the problem and how can it be solved?