closing workspace(s) means that MC is hanging

what could it be that causes MC to hang when closing a workspace ?
i use currently 567.973 ..

its hanging always when i close a workspace with an errormessage that pops up and says something like " the server is working at full capacity" then nothing happens anymore in most cases ..

system is : WIN2K with latest SPs and most of updates
datafeed : IB and / or IQFEED

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