You can narrow down the possibilties by explicitly casting your datatypes to the expected type for the signature

Just to let you know.... the vb6 instr functionality (in .net) is basiclly wrapping this:
VB Code:
  1. MsgBox(System.Globalization.CultureInfo.CurrentCulture.CompareInfo.IndexOf("TeSt", "S"c, 0, Globalization.CompareOptions.IgnoreCase))

String.InStr(also uses the CompareInfo Class to compare strings)

Using compareinfo gives you even more control...

if you still want to use vb6 InStr, post the line that you use it.. and I'll help you fix it...