ghostscript producing strange pdfs

[Maier Gerfried]

Hello!

I've two pdf's which I joined to one file using ghostscript (GNU 8.15). 
The resulting file can be viewed fine, but when printed with acrobat, 
most of the text are little squared boxes... (but the screen view is ok).

This behaviour does not appear with the original pdfs and is definitely 
introduced by gs, as the same thing occurs if I run one pdf through ps2pdf.

The documents were created using distiller and contain Arial as a 
TrueType font.

Does anybody have a hint for me?

Thanks in advance
Gerfried Maier