Cannot export AX project in AX7

I tried to export project from VS.  I succeed before.  But today I got a
Microsoft Visual Studio error message box saying "Value cannot be null.
Parameter name: filePath".

Finally I found my co-work added a dll as reference to my project before, and now the dll's location is changed in new environment, so VS cannot find the dll therefore the whole VS project cannot be expported.

Just remove the reference or correct its file location, then the VS project can be exported.