>I have many simulators and some utilities that send and receive data via a serial port. this works fine in windows xp but on windows 7 the utilities never receive any data through the serial port. If I switch to the modem serial port and pass ATZ, it returns with an OK immediately so I know it is working. If I put any of the simulators (that basically continuously send data through the port) on com1 and then put another utility/simulator that reads data on another com port (or on another machine on a comm port connected via a cable) , the one receiving never fires the oncomm event of the mscomm control.
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>Any ideas what would prevent data from coming in a serial port?

What happens if the transmitter is Win7 and reciever is Win XP? Have you tried using Hyperterm on the receiver side and see if you see any differences?