I believe this is hard to tell. As it states it is an "internal error", which pretty much means that it should not happen and the error is not caught as expected. It basically means that some property is in a state we don't expect at a specific point of time or position in the code.
Are you able to replicate the problem? In this case it would be beneficial for us to see the rule set and replicate the issue. If it happens sporadically, will it go away when you restart MWG?
Might this be relevant?
2012-12-17 19:19:01,824 [FATAL] Property with id 958983948408982 is missing
SOLVED. I figured out what was causing it and fixed it.
MWG 126.96.36.199.0 (13935)
- Internal Error 10056 appearing randomly and affecting all traffic traversing MWG
- GUI performance bad
- Show Referring Objects not working
- Deleting Lists not working
- Found ["FATAL] Property with id 958983948408982 is missing" in /opt/mwg/log/mwg-errors/mwg-ui.errors.log
- Found where that property was referenced in /opt/mwg/storage/default/[my current config date and time]/gwrs.xml and identified the items directly above and below the property. One was a ruleGroup, the other was a rule that happened to be the top rule in that particular rule set. Edited the criteria for the ruleGroup and found that although the current criteria was set to Always, it had at one point been set to the property that was now missing. Enabled the radio button for "If the following criteria is matched" and deleted the property that the GUI now referenced as "Missing property" for the property name. Saved config