Hi,
Its not that I'm not responding to this kind of error. I respond to any post where I think I can help someone. The problem is if I can't reproduce an error then its very difficult to fix a problem. Please understand I am involved with a lot of web sites running mojoportal and this error is not happening for me on any of them so it makes me think you are doing something different than me with your configuration or your environment but you are not telling me about it so I am not able to make this error happen and therefore can't find the cause of the problem.
Here is what I do know.
This error is occuring after you edit content when it executes code that should update the search index. The search index files live in the file system under Data/Sites/[SiteID]index where SiteID is probably 1 and 2 since you have 2 sites. The error could be caused by several possible things that I can think of and maybe others that I can't think of.
1. Are there any missing configuration files? There should be a configuration file for each feature that is searchable under Web/Setup/indexbuilderconfig folder. Also if the permissions on these files prevent the asp.net worker process from reading the files its the same as if they were missing.
2. The above issue seems most likely for this specific error but similar errors can occur if the search index is getting currupted. The search index can get corrupted if you have 2 physical sites using the same database and the same siteid. In this case editing content one site will update the search index for that site but the other site using the same database is now out of sync becuase it gets the same content from the db but its search index doesn't have the new content since it lives in the file system.
Item 2 indicates the kind of thing you may be doing different and not telling me, there may be others that I'm not thinking of so its important to tell me anything different or unusual about your setup or environment.
Hope it helps,
Joe