Some days ago I had to program a bigger import for a Drupal 7 Forum, including several hundreds of thousands of entries and comments. I decided to use the Drupal migrate.module as helper for this import and it was a good decision!
migrate.module made things much easier and reduced the amount of custom import code.
Anyway I had a little problem during multiple import tests. After the first import test-runs worked, the import didn't run through anymore and resulted in the following message (no error):
Processed 0 (0 created, 0 updated, 0 failed, 0 ignored)
I first thought there was a mistake in my implementation, but it wasn't. The reason seems to lie deeper within migrate.module and the solution is simple: You just have to reset that migration completely by removing it and re-including it again by using the
"Remove migration settings"
After this hard reset everything worked fine again for me, without any other changes.