The link below is from 2011 and for version 3.0:
super_star wrote: ↑
Thu Mar 16, 2017 2:10 amWhat actions did you take (updating your board; installing a MOD, style or extension; etc.) prior to this problem becoming noticeable?
I followed this viewtopic.php?p=12964891#p12964891
I'd be inclined to replace any files you edited while you were doing the above from your backups, check that that's good first.
If you go to ACP> Customise> on the left side you should have a link for Manage extensions. If you're not seeing that please post a screencap of what you are seeing.