The error implies that the sql stement in the VB application has taken longer than the time allowed by the application, by default this is 30 seconds. There can be many causes - poor database design, slow network, large amounts of data, deadlocks, error in the program code, under spec hardware and more.
Cant give any specific answers how to fix it without knowing the cause but heres a few suggestions -
Debug the code to identify the problem area and maybe post the relevant VB code.
Run the SQL Profiler may help to identify the problem area.
Check you have installed latest service packs for the OS, SQL server and MDAC.