Using <DllImport("dmsgen.dll")> _ with projectwise dll's

Hello,

  I'm trying to use VB.net with projectwise ,I tried to add some dll's from projectwise explorer to my project but it cause an error of "a refrence to this file couldn't be added please make sure this file is accessible and that is a valid assembly or com component", So I tried to use <DllImport ("dmsgen.dll")> _ then write functions but the datatypes cause errors example(LPCWSTR  and LPCWSTR) Any help about that??

Thanks,

Walaa