Hi,
The errors you are having are related to the site search index. Most likely the content updates and deletes are actually happening, but the error happens afterwards when it tries to update the search index.
I think there may be a problem with files under /Setup/ProviderConfig/indexbuilders
Please tell me the names of all files in that folder. Also you may need to check file permissions on those files to see if they are all readable by the web process user (the user that is the identity on the application pool in IIS). Possibly something about those files got corrupted or permissions change on them since it was working fine for a long time.
Other than that I would try to rebuild the search index. Do this by first backing up the folder /Sites/1/index, then delete all files from that folder and do a search and that will trigger it to rebuild the search index (as long as folder permissions are correct so it can write new files).
If all else fails it is possible to disable the search index and this would eliminate the error. You can do that by finding this to your Web.config and changing it to true.
<add key="DisableSearchIndex" value="false"/>
Just fyi, you are running a very very old version of mojoPortal, released over 3 years ago. However because it is so old it would be fairly challenging to upgrade. The version you have runs on .NET 2.0 which we no longer support and many things have changed in the way our skins aka design templates work so your current skin would need significant updates.
Hope that helps,
Joe