I do not understand you clearly: "Program hangs" means that user inerface hangs and you need Task Manager to close it or means that program hangs to respond to modems, but interface works normally?

If program hangs to respond to modems: Two years ago I trying to write application, which communicate with many ECRs (typically 16, but up to 80!!!) through one COM port in semiduplex mode and also with fiscal printers. In VFP this was impossible: application cannot run enough fast to keep synchronisation with one ECR/fiscal printer even on 1200bps. Because I must provide speed of 4800bps, I wrote this application in VB and everything works well.