SP2010 - Search Crawl not working on remote services farm

A quick post on two issues I've encountered lately. Both are related to SharePoint 2010 Search crawls that suddenly stopped working.
I'm just going to post the symptoms and what worked as solution for me.

The SharePoint set-up consists of two farms:

• Farm A hosts the collaboration web-applications, in which the users upload their documents
• Farm B hosts most of the service applications, including the search service application(s). These search service applications crawl content from Farm A. Furthermore, these service applications are consumed on Farm A (so people on that farm can search the crawled content).

Issue #1
The crawl log was filled with the following errors when crawling farm A:
The SharePoint item being crawled returned an error when requesting data from the web service. ( Error from SharePoint site: Value does not fall within the expected range. ).

Solution
Apparently there was an issue with the web-apps that were being crawled. In order to get them crawled again, I

1. Detached the content databases linked to the web-apps on farm A
2. Removed the web-app (make sure to delete the related IIS site)
3. Recreate the web-app
4. Attach the old content db again

Simple as that.

Issue #2
Some weeks later, my crawl log got filled with this lovely message:
The SharePoint item being crawled returned an error when requesting the data from the web service. ( Error from SharePoint site: *** Could not find part of the path 'c:\TEMP\gthrsvc_OSearch14\{random-text}.tmp' 

Solution
Despite the error, that path was indeed present on all my machines in farm B. I tried fiddling with the permissions on that folder, but nothing helped.

In the end I just:

1. Removed the consumed search service applications on farm A.
2. Removed the search service application(s) on farm B
3. Recreated the search service application(s) on farm B. Luckily for me, I had already scripted this procedure in PowerShell.
4. Publishd the service apps again on farm B and consume them on farm A.
5. Recrawled all content

Conclusion: if some part of SharePoint is fucked up, you can usually fix it by removing & recreating it :)