Problem:
I got the vxdiag vcx se bmw scanner working with the ISTA+ 4.35.20. It failed to read VIN, and manual input also failed. No communication with a 1999 BMW model.
Here is the clue.
VXDIAG VCX BMW cannot do vehicles that old especially K-line models.
It works better on 2005 onwards BMW. Same as other brands.