Conversion Failure

Hi, I tried to get a number of Photoshop files converted to pdf's Each file was around 30 MB and is for a book that I want to self publish. Happened last night when I tried to get 5 files done - each after a VERY long upload time quoted Conversion Failure and when I moused over I got a message:

The file has not been processed.

An error has occurred which stopped the processing of the PDF

I tried again tonight with another file and after about 40 minutes of waiting got the same message.

I did one conversion from a jpeg of 2.7 MB and that worked. Sadly printer has requested that I continue to convert from a psd > pdf.

What am I doing wrong and can you make any suggestions so it will work. I have 36 files to convert - HELP!!!!!!!

Thanks