Debugging mount error 13

I'm connecting a new PC to my network and need to be able to move files
across to it. However, when I attempt to mount a directory from it, I
get the dreaded "mount error 13 = Permission denied message.

My mount command has uses a credentials file with the correct name and
password in it, and everything else appears to be hunky-dory. There are
no warnings given, just the error message. I'm using a script I wrote a
couple of years ago, and which I use, successfully, every day.

Any tips on the direction I should be taking to debug this would be
gratefully received, particularly ones enabling me to determine which
machine has the problem,

-- 
 All the best,
 John