As your server seems to be running some Unix variant (I'm going by the "/tmp"), you probably want to specify the path type (otherwise, "File::Basename will assume a file path type native to your current operating system...", i.e. $^O will be inspected).  In this particular case

fileparse_set_fstype('MSWin32');
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(This of course assumes that the filename actually comes in as C:\Documents and Settings\... (with backslashes). In other words, to debug this, it's probably a good idea to just check (print out) the value of $FileName before you pass it to fileparse().)