How to use a dll in a QT

Dear All,
I need to use a external dll and its functions in my QT application. I tried for days but failed. The application that I developed gives "collect2: ld returned 1 exit status " error. I could not find a way to resolve the problem. Application project files attached. Any Help?

Operating System:Windows7
QT:QT Creator 2.01 Based on 4.7.0, 32 bit

Regards
Cengiz EKEN

I think you should to replace string containing visa32.dll with visa32.lib in LIBS section in your .pro file. Isn't it ?