Your are wondering why you cant add offline files to your seach index
When you look at your indexed locations and hover over your offline file locations you see the tooltip
indexing of offline files has been dsabled by your systems dministrator
or words to that effect
This implies that there is a policy restricting indexing of offline files being applied either locally or from the Domain Controller the computer is registered to (if at all).
Get your admin to check the group policies applied locally and from the DC, paying particular interest in the location
Computer Configuration/Administrative Templates/Windows Components/Windows Search
Ensure “Disable indexing of offline files cache” is not configured.
Another problem i encountered was, offline folder changes were not working, MS Excel and Word was hanging when trying to save to an offline location, yet notepad could happily save a txt doc to the location.
As it turns out, its an NT authentication issue, if you are able, set the security on the root folder of the offline folder so that Domain Users have full control, cascade these permissions to all child objects and then try your tests with excel word and folder changes. This worked for me.