SQL handles mapped drives very difficultly. You won't be able to see the mapped drive unless the same login was used to create it. The only way I've been able to used mapped drives is to perform the mapping from within QA via xp_cmdshell 'net use m:...'

There are other ways around it but this is the safest way for me to do it. Generally I use UNC paths (\\server\share) to write to network drives and this has given me no problems.