I can successfully import Asta Powerproject project files. Then I do some stuff with it. And finally I have to export the data again to Asta Powerproject.
It seems like Asta Powerproject doesn't want to import neither MPX nor MSPDI files. Is there a way to export the data to a file that Asta Powerproject can import?
A quick test suggests that indeed Powerproject doesn't like valid MSPDI and PMXML files generated by MPXJ from a Powerproject PP file. i.e. these are files which will happily import into Microsoft Project and P6 respectively, but cause failures when an import into Powerproject is attempted.
You can see a minimal amount of failure logging in the Windows event log, but not enough to diagnose the issue. The PMXML import seems to get a bit further than the MSPDI import, and fails when the new PP file is being written. This appears to leave a log file in C:\Users\<user name>\AppData\Local\Temp which may shed some light on what it's having trouble with.
One way to address this might be to raise a support ticket with Elecosoft: they may be able to fix the issue on their end, or at least suggest what is causing the problem.
The other way to tackle this would be to export your PP file from Powerproject as an MSPDI or PMXML file and compare the structure with what MPXJ produces. You'd then need to start replacing the Powerproject generated content with MPXJ generated content element-by-element (or vice versa) until you trigger the failure when importing... which might lead you to the problematic data. Unfortunately it'll be a bit of a painstaking process.