oscilloscope connected through rs232 serial port

OS Win98SE
BorlandC++Builder5

Hello, digital oscilloscope is connected via null modem cable to PC serial port.
Serial port is opened with CreateFile and handle is got, but i cant read answer or write commands to oscilloscope.
I get SystemError 6 = invalide handle. Although in another functions (SetCommMask for example) this handle is true.

1) Do i need second handle to oscilloscope?

2)I need ideas how such comunication must go on?

Oscilloscope has owne driver - TekVISA.
But i have linking errors - unresolved external viOpenDefaultRM for all functions in it (Include and Library paths are included ).

Thanks for all advices, references, ideas.