RH 2015 cmd line: Error: Failed to scan all the project files. Unexpected Error: Failed to prepare single source data for RHCL.

I ran into an issue that folks had previously reported already for RH11 (see RH 11 cmd line: Error: Failed to scan all the project files. Unexpected Error: Failed to prepare single source

My project generates the configured SSLs just fine from within the RH2015 GUI. I migrated the project from RH11 when the command line still worked. Migrating to RH2015 gave me a lot of hassle but I eventually got it working. Now, my last hurdle to overcome is getting the command line build to work.

The error on the command line simply states. It pretty much occurs right away:

Error: Failed to scan all the project files. Please use RoboHelp to recover the project.

Unexpected Error: Failed to prepare single source data for RHCL. Please try to compile it in RoboHelp.

I have not yet tried the recommendation from the linked discussion where people suggested to verify each and every .FPJ file and make sure it's consistent with the file system. My project has 128 of those and 500+ topics. So, I would appreciate any tips how to automate that work and/or what other things to try first in order to get the command line build to work.

Thanks,

Wolfgang