Hi I'm using the WriteFile and ReadFile WINAPI to write/read from a COM port periodically. The protocol is : first wirte to a port and then read the response from a port (=device). The write operation occures every 50 msec at least. Every second attempt to call WriteFile fails and GetLastError returns ERROR_OPERATION_ABORTED. Then I use PurgeComm to clean a port after the failure. The next call to WriteFile succeedes, ReadFile succeedes, and the next try to write is cancelled and so on. Does anybody know what can cause this error? Thanks :(( Natalie