The bug isn't fixed in 5.2.2, I believe it is fixed in 5.2.3.

Roger

I also upgraded to 5.2.3 and am still getting the errors today.

AssemblyVersion: 5.2.3
PortalID: -1
PortalName:
UserID: -1
UserName:
ActiveTabID: -1
ActiveTabName:
RawURL:
AbsoluteURL:
AbsoluteURLReferrer:
UserAgent:
DefaultDataProvider: DotNetNuke.Data.SqlDataProvider, DotNetNuke.SqlDataProvider
ExceptionGUID: 78a540f9-26f8-4dec-97f1-91c81c03f795
InnerException: Access to the path '\Cache\Modules\' is denied.
FileName:
FileLineNumber: 0
FileColumnNumber: 0
Method: System.IO.__Error.WinIOError
StackTrace:
Message: System.UnauthorizedAccessException: Access to the path '\Cache\Modules\' is denied. at System.IO.__Error.WinIOError(Int32 errorCode, String maybeFullPath) at System.IO.Directory.InternalCreateDirectory(String fullPath, String path, DirectorySecurity dirSecurity) at System.IO.Directory.CreateDirectory(String path, DirectorySecurity directorySecurity) at DotNetNuke.Services.ModuleCache.FileProvider.GetCacheFolder(Int32 portalId) at DotNetNuke.Services.ModuleCache.FileProvider.PurgeExpiredItems(Int32 portalId) at DotNetNuke.Services.ModuleCache.PurgeModuleCache.DoWork()
Source:
Server Name: WEB22

----------AND------------

THREAD ID: 6
TYPE: DotNetNuke.Services.ModuleCache.PurgeModuleCache
EXCEPTION: Access to the path '\Cache\Modules\' is denied.
RESCHEDULED FOR: 2/18/2010 9:22:09 PM
SOURCE: STARTED_FROM_TIMER
ACTIVE THREADS: 0
FREE THREADS: 1
READER TIMEOUTS: 0
WRITER TIMEOUTS: 0
IN PROGRESS: 0
IN QUEUE: 6
Server Name: WEB22

What 3rd party modules are loaded on the sites that experience this error? The only 3rd Party Modules are: Ultra Video Gallery 3, and Effority User Directory

What do you have PurgeModuleCache set to run at? Need to know the Frequency and Retry Time Lapse values.  See below

Also, do you have any other Scheduled item that runs directly before or after or at the same time as PurgeModuleCache?

I've never messed with the Scheduled item defaults (that I recall) because I don't really know how to use them.  Here's a pasted table:

How much traffic do your sites generally get? dozens, hundreds, thousands of users per day?

Dozens at most.  Mostly used as a small "intranet"

Finally, what account(s) have you set on your web folder(s) and what permissions have you set?

I'm not sure what you mean?  I have 3essentials hosting and can ask them to double-check permissions if I know what to ask them... but this wasn't a problem in the event log in the past till I upgraded to 5.2.2 and I didn't change anything with permissions.