That resolved the issue. Thanks for the hint. Lars On 2013-03-28 18:17, Joey Adams wrote:

Try upgrading to the latest network package.  There's a bug prior to version 2.4.1.0 where 'connect' blocks other threads from running, because the underlying FFI call was marked "unsafe".

Somewhat unrelated, but if your program needs to run for long periods of time (e.g. a server), you're in for a nasty surprise: GHC currently doesn't support interrupting network I/O on Windows.  After about a thousand hung connections, the program will run out of address space and hang.  A partial workaround is to use socket timeouts; see setHandleTimeouts in the network-socket-options package.