Plugin Errors are adjustments to plugin records which often cause problems on their own or when used in conjunction with other mods. These occur by mistake or due to bugs in modding tools. Some errors can be benign, or included intentionally in a mod for it to function correctly.
Some plugin errors will cause crashes, particularly in combination with other mods. Most plugin errors have the potential to cause unintended things to happen in game.
These are errors which can cause problems in certain circumstances.
Identical to master records (ITMs) are override records that are identical to their master. That is, a record with no changes. ITM records provide no new information to your game and can override information from other mods due to the rule of one.
Any time a modder selects a record in the CK it will be mark it as "edited", which saves it as a record in the active ESP, even when no values in the record have changed.
It's best practice for modders to edit a non-critical record value (such as EditorID) if they want to indicate an ITM is intentional (this makes it no longer an ITM).
Identical to previous override records (ITPOs) are override records that are identical to the previous override. This happens when a mod makes a change, but that change is identical to what the mod before it changed. These are very similar to ITMs, and usually occur in the same fashion.
Unexpected reference errors (UERs) occur when a record references another record in an unnatural or abnormal way (such as a crafting recipe creating a weather type). Sometimes these usages are actually valid such as harvesting a plant giving the player a key. When a UER is valid it's best to alert the xEdit team so they can update xEdit to not report that reference as an error.
Unresolved reference errors (URRs) occur when a record references a FormID that cannot be resolved. These error messages are displayed as: "Error: Could not be resolved" messages when checking for errors in xEdit.
The game engine usually treats URRs as NULL references, but they may cause issues in certain circumstances.
These errors usually occur when a modder removes records from a mod without cleaning up all references to those records, or when a mod's masters change.
Dirty/wild edits (DWEs) are unintentional record edits. Wild edits are not ITMs, so automated cleaning tools have no way of cleaning them. Wild edits have to be found and resolved manually.
If a modder doesn't review their plugins, they may publish them with DWEs. These most often occur with object references in interior or exterior CELLs, with objects being moved slightly.
Other errors (OEs) is a designation for any other types of errors that don't fall into the other groups. There are a variety of other errors that are reported by xEdit, such as missing quest aliases and unknown flags. Some OEs are safe to ignore.
These are errors that often lead to crashes or glitches, and should always be fixed.
Deleted reference errors (UDRs) occur when a reference is marked as deleted. Deleted references can cause crashes if another mod refers to them. Most UDRs can be automatically resolved, but deleted navmeshes can’t be, and can be extremely difficult to fix without rebuilding the entire plugin.
Unexpected subrecord errors (UESs) occur when the data format of a record is abnormal. These happen when a record was produced or altered by a third party tool improperly (such as TESVSnip). These errors can sometimes be fixed by opening the plugin in the CK and re-saving it. When that is insufficient the only solution is to completely rebuild the plugin.