By default the Sitefinity search index management screens are dynamic. This means that when you create a new search index Sitefintiy will query all active modules whose content can be included in the index, and present them as an option for you to select.
However once you define a search index, the selected modules are saved for this particular index. This means that next time you go in and try to edit this search index Sitefintiy will know which modules you have selected, and will try to access their "pipes" - these are the classes that are responsible for pulling data into the search index.
The most probable reason for getting the "No pipe registered" exception when opening a search index that has already been created, is if one or more of the modules that were initially selected to be included in the index are not active anymore. This means that they have either been:
a) disabled from Administration->modules and Services screen
b) removed from your SystemConfig.config (you will not see them under Modules and Services screen)
c) you have changed your license with one that does no longer support this module
d) if it is a custom module there is an error preventing it to be initialized
e) if it is a Sitefinity out of the box module and there has been an upgrade issue that is preventing it to be initialized now
f) if you have customized its InboundPipe and registered a new pipe that is having problems
I have tried listing the above factors in the order of relevance to what could have caused the problem on your end.
You can easily cross out some of the possible reasons (a-c) by trying to create a new index - if this screen shows no errors then the problem is most likely one of the three listed first. You can safely delete the original search index and recreate it.
If you are observing this error even on new search index creation then please elaborate if you might fall in one of the scenarios listed after c) above, and check them one by one to confirm if this is not the case.
If any issues still persist, please remove (or move) all files from your App-Data/Sitefinity/Logs folder and try reproducing the problem again - if any new logs are created in the folder that you just cleared, please send them over to us for further investigation.
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