The latest update of NextGen wreaked havoc on the WordPress menu option to link or delink (buttons faded out).
Either it allows one link per post and is removed or allows none at all.
The workaround is to either make a word Bold and then link or Alt/Shift/A.
But workarounds are frustrating when you have as many sites as i do.
Definitely NextGen as it happened on 4 of my sites. Hoping for solution. Thanks.