Can"t write to a network drive

[Cheng]

 I am using the log4net"s FileAppender. It is perfectly fine when the logfile
 is set to a directory in the local hard drive. However if the logfile is in
 a mapped network drive, log4net refuses to log anything and there is not any
 error message either. Is there any way to solve it?
 
 Here is the config for lcoal drive d:\
 <param name="File" value="d:\\logfiles\\Log.txt" /> it is working fine.
 
 here is config for a mapped network drive U:\ <param name="File"
 value="U:\\logfiles\\Log.txt" /> which doesn"t work.
 
 Thanks