Yes, sorry about that; the Outlook Connector switched to the ost-file format
again. You should then of course use scanost.exe but I guess you knew that
already?
Are you running any startup applications that rely on Outlook? For instance,
mail sync software (connected mobile device?), fax software, Skype, etc...
These applications could directly place a lock on those files. Either
disable their integration with Outlook, close them or prevent them from
automatically starting up to be able to scan the ost-file.
As for the removing part; you could also opt to create a new mail profile
with only the Outlook Connector as an account in order to test if it has any
effect with the new mail profile.