I've updgraded a system to kdepim 4.6 and I haven't been able to get Local Folders to work. I tried pointing it at the old Local Folders but that didn't work, I created a new directory with the appropriate folder but that was no good. When I try and send an email it compains about "message has invalid sent-mail folder";

When I change the configuration on Local Folders to another directory it give the followind error
QMetaProperty::read: Unable to handle unregistered datatype 'KUrl' for property 'KUrlRequester::url'
QMetaProperty::read: Unable to handle unregistered datatype 'KUrl' for property 'KUrlRequester::url'
QMetaProperty::read: Unable to handle unregistered datatype 'KUrl' for property 'KUrlRequester::url'

I'm not quite sure what you are trying to do but at one point I found that I had to Import Messages from an older version of KDEPIM; this then created a new set of folders and I then had to copy the contents of each imported folder into the equivalent new folder. Tedious but it worked.

Yes, I ended up doing something like that