finding errors for communications issue

All--

Having a bit of time with this, hoping perhaps someone can please advise 
on path(s) to follow toward resolution...

Have a 3rd party communications application running on an intel server 
which works fine, receiving and sending files with a remote partner using 
SOAP over HTTP. 

It works fine, that is, as long as the place where it's configured to put 
those files is local to the machine where it lives. As soon as a folder 
on the AS/400 is mapped on the intel box and the application is 
configured to use it instead of the local folder, the application starts 
sending the files it receives to its discard bin, which the vendor says 
happens because of issues when attempting to  write the file. 

Along the way to attempting to resolve this, we've defined new users with 
matching id/password on both systems, so now when mapping the AS/400 
folder no signon is required. The files can be manually copied to and 
from the AS/400 folders from explorer with ease. 

We've also tried mapping a folder on another intel box instead, and it 
works fine that way. 

So the thought is that the 400 must be kicking it out somewhere along the 
line and for some reason, that this event must be logged, and that if it 
is found and read it may lead toward the resolution of the problem. 

Not being very deep on this sort of stuff, where should such an error 
message be found? 

tia, 

--Jerome Hughes