mixing FM13 and FM12 is no issue in your case, as long as no new FM13 functions are supposed to run on FM12.
This looks like a Windows 7 conflict with User-Access-Control (UAC).
Select the entire folder of your FM-Solution, right click mouse to enter contextual-menu and go to the setup? (Eigenschaften).
set checkbox off for write-protection, go to security and set 'full-access' for all users and groups. (Maybe someone will help you with proper translation since I have german version of Win 7 only)
As far i know, this is a known behavior and you have to unlock the Device (iPhone, iPad), before launch the transfer.
Let us know,
Yes this is a known so called iTunes "security feature" that drives every one nuts. It's an issue with iTunes, not FileMaker. As Fred indicates, just enter your passcode to unlock the iOS device and this error message will not pop up until the iOS device sleeps and then you have to unlock it again.