I'm porting a modem application from Windows 98 to Windows 2000. The application uses a modem to connect to another device using a phone line. The problem i encountered is that on Windows 2000, the exact same communication code used on Windows 98 fails. Before jumping to conclusions, rest assured that i've double checked the comm port initialization (it's an external modem) and the modem gets the right commands and correctly dials the number. Still, when it gets to sending some bytes of data to the device at the other end of the phone line (also kind of modem, obviously), it fails to do so. Somebody suggested this might be a timing issue (the device must get a reply in a short period of time, around 200ms), but i've logged the data packets and their delays fall within the specs. The speed i'm using is 300 bauds and i'm transmitting/receiving only a few bytes (at most 10 bytes at times). Has anybody encountered a similar problem? Could this be a timing problem but at a lower level? (maybe some serial driver internal delays i'm not aware) Please suggest any workarounds, because i'm out of ideeas. Thanks in advance for any help!