After the migration the password protected directories are not working. This is because these passwords are not started in the psa database, instead these password are stored in file system in md5 format. After the migration it fails to retrieve the md5 encrypted passwords from the file system.
To solve this we have to manually update the passwords after the migration, then users will be able to login to the protected directories.
NB: This is bug in plesk 11 version and is fixed in the later versions.