Shared folder as network drive, some files cannot be written

I have a folder on C:\, let's say C:\ABC, shared as a network folder as R:\ with full access (to this directory and all its contents) to all users. (Win2008R2)

Inside the folder I have one specific dir which I have made a site of in IIS7 (functioning well).

In the mentioned subdir there are batch files to be run every night, so we have made scheduled tasks for them, HOWEVER:

• When running them from Task Scheduler, for some we get (0xFFFFFFFE), which I think is related to network drive access
• When starting the problematic ones manually, the error message says that the log file couldn't be appended because it is used by another process (and is not...)

What makes me think that this is a shared folder issue? Well, on other servers we have the same setup, except WITHOUT shared network drive and there are absolutely no issues whatsoever.

Has anyone met this kind of problem? And if so, what could be done about it? Thanks: Attila