[Mobhack]

Did you start the PBEM on the previous edition of the game?

OOBs have changed, and the standard "don't install any patch if you have an ongoing PBEM" naturally still apples. Just that now, you will get an OOB warning in basic security mode too.

Otherwise - check that your opponents "new install" is fully patched up and the same level as yours. The version number is reported on the front page of the game. (My guess is on your opponent not having patched up). If he has, also ensure that he has not installed any custom OOB set affecting the OOBS in use in your PBEM, or done any OOB editing (even changing of unit names, adding new formations etc).

Andy