ProjectWise Explorer CONNECT error: 112173 Cannot start application for the specified document.

Have you looked at this article and tried the trouble shooting steps suggested? Trouble-Shooting Office Integration - ProjectWise Design Integration Wiki - ProjectWise - Bentley Communities 

This is an age old problem with all versions of ProjectWise and Office. There seems to be really no consistent condition that triggers the issue. Also there seems to be no consistent fix from one user to another except one. This is a user level issue meaning, that if you login to that computer with a different account the issue will not be present.

When I have thrown every trouble shooting procedure at it and they have all failed, I leave the user with 2 options:

1. Open the document with non-integrated Excel/Word. This works fine except occasionally the user will not be prompted to check a file back in.

2. Delete the user profile and have the user log in again.

The second option has not failed to resolve the issue, though most users shy away from that fix and understandably so.

Adding the ProjectWise and install directories as trusted locations is a useful step and I have had more luck with that one recently that the others.

The regedit fixes are hit and miss.

Hope this helps.

Reinstalling Office finally solved it.

Reinstalling Office finally solved it.

Oh great. I have never tried that. Good to know.

Another line of attack!