rsync - Jun 2004 - problems when using multiple clients

Hi,

I'm using a rsync server ( v2.6.0 / cygwin 1.5.7) on Win 2k Server and
rsync clients (same version) on several Win-NT 4.0 machines in order to
distribute files to several machines. Doing simultaneous rsyncs from up to
4 clients works fine whereas simultaneous rsyncs from for example 15
clients are only successful for the first few clients. For all remeining
clients it seems that no synchronization has been done. They kept their
original files as if there would have been no difference between new and
original and rsync did not issue any error.
The rsync parameters are: -vvaz --progress --timeout=60 --partial --force
--bwlimit=12 --delete
Did anybody experience similar behaviour or have any ideas about it?

Thanks
Thomas