"This is actually a diagnostic message that is not in fact an error per se. Exchange includes a number of diagnostic logging functions, including diagnostics for internal caching. Details on the Table Cache are hard to come by, but it appears to be a cache of memory in Exchange that's used for caching the results of specific data tables. The diagnostic message in question refers to actions involving the cache itself.
Since this level of diagnostic logging is useful only when heavy-duty debugging is being performed, it should not be left on all the time. The log may get flooded with these "errors, " which are not in fact errors, and may crowd out other, more important messages. By default these diagnostic logging actions are disabled. Some more information on diagnostic logging is available in the Exchange online documentation, at exchsvrdocsHTMXMTAA004.htm in your Exchange installation.
To turn off this level of diagnostic logging, open the Exchange Administration program, then open the Servers container, select the name of your server and hit Alt-Enter to bring up its properties page. Under the Diagnostic Logging tab, expand MSExchangeIS and select System. Look for Table Cache and set it to None." See W2K Tips link below.