Something is wrong with the WsusScn2.cab file. Delete yours from your BatchPatch cache directory (as defined under ‘Tools > Settings > Windows Update > Local update cache directory’). Then use ‘Tools > Download Microsoft offline scan file’ to download a new one from Microsoft.
Thank you for the quick reply! I’m not sure why, but explicitly adding my BatchPatch user account to the c:\program files\batchpatch directory made it work (even though the account is a member of the local admin group).