If you are getting “Couldn’t Complete” message from the solution checker, verify you can export the solution before running the solution checker. That way you’ll be able to see what’s wrong instead of an unhelpful “couldn’t complete” message.
I created a solution recently in a test system and ran the solution checker but I constantly got a “Couldn’t Complete” message. I logged this with Microsoft who, as ever, needed to see me run the checker and see the message before they’d look for what was wrong. The answer from Microsoft in the logs was:
Microsoft.Crm.CrmException: Failed to export Business Process "Compliments Process" because solution does not include corresponding Business Process entity "aaw_complimentsprocess". If this is a newly created Business Process in Draft state, activate it once to generate the Business Process entity and include it in the solution.
So I tried exporting the solution as unmanaged and got the same error message as Microsoft had found. My BPF was published but I used “Add Required Components” to add the associated entity. I then tested that I could export the solution, this time it worked and then the solution checker could also complete and give me a set of results. So check you can export a solution before you run solution checker as that way you’ll be able to see what’s wrong rather than a just couldn’t complete message.