During migration, the error above is only shown for Driver packages
because Migration Manager needs to process some content in the source path, so it will fail during the migration itself. If you migrate a regular software package, it will succeed no matter whether the destination site has access to the source path or not, but later, SMS_DISTRIBUTION_MANAGER (distmgr.log) which starts up to process this package, will fail due to insufficient permissions on the package source path.
For more information see the following:
How to Import Windows Device Drivers into the Driver Catalog: http://technet.microsoft.com/en-us/library/hh301101.aspx