if shared drives are the only way for your environment to work with, then by all means i hope your company is using a DFS structure.
without DFS, your users will scream at you when the server goes down.
with DFS, is one of the DFS hostings servers is down for maintenance, other will pick up the redirections
not 100% foolproof, but still better than mapped drives or UNC as Clay pointed out.
Besides, can the user having the issue still put anything else in these folders? maybe it's an ACL permission on the fileserver itself?