The only thing I can think of is mod_security, though that would usually also stop you from saving.
I guess it could also be an overloaded or misconfigured server that's failing to do all the successive writes to the various cache files. You might check the PHP error log to see if there are errors occurring at the same time as the ones in the MODX error log.
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PLEASE, PLEASE specify the version of MODX you are using.
MODX info for everyone:
http://bobsguides.com/modx.html