The semaphore timeout period has expired

[teognost]

I have a step which copies files from a network location to another network location (size approx 100 Mb)
The copy step fails after approx 1 hour and 30 mins with this message:

2/18/2011 2:50:54 PM: Building project step 1119 - Copy install kits to Sydney Latest folder...
\\hqt\Public\NGKits\10.1.1315.0\ -> \\syd-01\Public\NGKits\NGLatestKits\
Copying: Setup.exe
Error copying file '\\syd-01\Public\NGKits\NGLatestKits\Setup.exe': The semaphore timeout period has expired.
0 file(s) copied
2/18/2011 4:11:11 PM: Step '1119 - Copy install kits to Sydney Latest folder' failed

First thing I do not understand is what is causing this problem.
Second thing –why if the step failed –I still have in the target folder (\\syd-01\Public\NGKits\NGLatestKits) a corrupted version of Setup.exe
Maybe someone could explain ...
Thanks