The application builds but the error is thrown at runtime.... [closed]

Question

I'm sure ChangeFolder is still present... That's what's so odd. The application still builds so Visual Studio recognizes that the method exists but the error is thrown at runtime. We are not doing anything with the return string but that should not be relevant.

The line of code throwing the error is about as simple as it could be.

ftpManager.ChangeFolder(folderName);

Any idea what could be causing the error?