ABBYY FlexiCapture rule error - System.BadImageFormatException: Bad IL format
Symptoms
In ABBYY FlexiCapture you may see a message similar to below. The message has nothing to do with the field in question but instead indicates that the rule itself could not load.

Cause
ABBYY FlexiCapture scripted rules are compiled into small files called DLL's. These DLL's use an Intermediate Language (hence "Bad IL format").
The error message is an indication of a temporary issue where FlexiCapture could not properly load the DLL with the rule
Resolution
This error is unlikely ever to show so it's worth reporting a ticket if you see it but there is a simple workaround.
Within a document you can hit Ctrl-F6 (also via the menu `Tools... Recheck rules (Ctrl+F6) option). This forces FlexiCapture to re-run the rules on a document which will also force it to re-load the DLL.
Within a list of documents, e.g. within a task, you can do the same. Select one or more documents and Ctrl-F6.