Reported by GTC at https://www.qb64.org/forum/index.php?topic=3459

Opening the COM port with OPEN "COM" + Port$ + ":4800,N,8,1" FOR RANDOM AS #1 causes any attempts after the first open and CLOSE to fail with error 64.

Changing the command to OPEN "COM" + Port$ + ":9600,N,8,1,CS0,DS0" FOR BINARY AS #fh behaves correctly.

The use of BINARY or RANDOM makes no difference, only the presence or absence of the extra flags.

Windows 7, 64 bit.