The original Vantive product (VBA and stored procedures) hasn't been supported for years. Vantive was purchased by PeopleSoft in 1999, and the Vantive product line was replaced in 2001 by PeopleSoft CRM 8.0. PeopleSoft was bought by Oracle, which no longer has any support at all for the original Vantive product.
The last fully supported Vantive client environment was Windows 2000. The client can run on Windows XP, but it has trouble when used with service pack 2 or later. I've never tried to run the Vantive Client on Windows Vista, but I'd be surprised if it worked.
Running software that is over eight years past "end-of-life" is always a gamble, and it looks like your luck may have run out.
In theory, theory and practice are identical. In practice, theory and practice are unrelated.