I get this error using the MSComm Control Ver 6.0 with mscomm.
When I use the same control on my PC it works OK.
I am using NT4.0 on my PC SP3 and NT4.0 on my laptop SP5.
If I set an Invlaid Port No it errors as you would expect but if I set a viable port I get the above error (8015). The setting of the port match the settings on my PC.