The same exception report value is being imported into a module twice. You can find these in Hyperview by looking for the tag then clicking on the AI/L or equivalent entries for the CAD sheets.
This is a serious problem if the import block is in use, because one of the values is always frozen. When you switch to the redundant module, as you do for a configuration change, the one that was working freezes and the other begins working.
In the case of analog blocks, the value will 'flat-line'. In the case of digital inputs, the imported value will simply fail to respond to a change in the source. This can be catastrophic.
Here are some examples from real systems.
--Generating index: Module 4,14,03 Block Index Duplicate off-module reference (AI/L, AI/L) to Module 4,14,03 Block 1669: 4640355 and 4640355
Digital inputs are even more of a problem, as you can never see that there is a problem until the frozen one fails to change when it should.
Duplicate off-module reference (DI/L, DI/L) to Module 1,01,17 Block 5947: 1021793 and 10217A6
To find the duplicate:
If both blocks are unused, there is no real problem.
If either block or both blocks are used, the problem is that one of the two import blocks is always "frozen". It does not work.
An important additional fact is that the situation changes if an "on-line" configuration is carried out. This legal operation will cause the import block that is working to freeze, but the frozen import block will start working. This applies even if one block is unused, as when it is on the spare blocks page.
You cannot tell which one is working unless it is an analog value, in which case one of the import blocks should be changing while the other stays unchanged. In the case of digital import blocks, you only see the problem if the input changes. One of the import blocks will not change when it should.
This error can be built directly into Hyperview. For more information, see the article Building error reports into the M14.