Failed to update setting value!

When trying to update items such as config, or add a new page, I very often get a successul message like this:

Action was completed successfully!
- Please wait while MODx cleans up.

This is often followed by the central section of the ModX admin control panel showing the following message, in plain text, alone:

Failed to update setting value!

The operations have been successful, the config is update and the pages are created etc, but it’s annoying that the pages don’t return to where they should.

I’d be grateful of any advice.

Specs:
modx-0961p2
Red Hat Enterprise
Apache 2
php 4.3.9
MySQL 4.1.20
Safari 3.0.4

Try searching for similar errors first. Safari is the issue here... http://modxcms.com/forums/index.php/topic,21243.msg131271.html#msg131271

Thanks, but it does refresh on after the "cleanup" message, but fails with the message I quoted. I searched the forum but could find no-one else with that error message in a similar scenario. Granted, it may be Safari, but I would have expected the poster of the thread you pointed out to have quoted the failure message if they had seen it - so I believe this is something else, although possibly related.