[solved] TB5 upgrade woes

After upgrading to TBP 5, I can no longer access my existing profile. I've checked prefs.js and it seems just like it was before, with all my mail account and newsgroup information. Just in case, I copied over a backup of prefs.js and it made no difference whatsoever. I also restored from a backup I'd taken with MozBackup, again no change. I've also done a complete disk check and it has shown no problems.

ThunderbirdPortable displays the splash screen and then disappears for up to five minutes, during which time it seems to carry out an enormous amount of I/O. Checking on Task Manager I can see it carries out over 2GB of reads and writes. After this, it takes me through the new profile creation process.

I've tried this on Windows 7 Professional, Windows Vista Home Premium and Windows XP Professional Service Pack 3. The same happens on each.

Does anyone have any idea what might be going on here? Why is the ThunderbirdPortable.exe launcher carrying out so much I/O?

---UPDATE---
I've just discovered that runlocally was set to true in thunderbirdportable.ini. Setting it to false solved the problem. FWIW, its not something I've ever changed before now.