Not sure why the MODx news and Security Notices RSS is slowing my Manager Area

So this has been happening a lot here lately with my MODx sites (0.9.6.3). The RSS feeds below have been making my Manager area of MODx go soooo slow.

RSS News Feed: http://feeds.feedburner.com/modx-announce
RSS Security Feed: http://feeds.feedburner.com/modxsecurity

Once I go to Tools >> Configuration >> Site and then scroll to the bottom and remove the feeds, the Manager runs fast again.

I logged into cPanel and checked my Error log, and here’s an example of what I see:

[Wed Apr 22 06:58:24 2009] [error] [client 70.214.19.222] Cache unable to open file for writing: /home/admin/public_html/******/assets/cache/rss//2552d997701d0d006f31cce7d173cba6, referer: http://*********.com/manager/

This has happened on several of my sites here lately. Anyone else having this problem?