Describe the bug
Unable to add files to some series:
Army - Behind the New Frontlines
Cops
Dice
Lockup
All result in Request Failed. GET /api/manualimport: Sequence contains more than one element
Logs
sonarr.debug.txt
sonarr.trace.txt
sonarr.txt
System Information
Do you have multiple series similarly named (or duplicates in general, somehow)? Sonarr is failing to look up the series by it's clean title which is essentially an all lower-case representation with most characters removed.
Without seeing the contents of the database it's hard to say, but you could check the Sqlite DB for dupes with:
CleanTitle,
GROUP_CONCAT(Id, ',') AS Ids,
GROUP_CONCAT(TvdbId, ',') AS TVDBIds,
COUNT(*) RecordsPerGroup
FROM Series
GROUP BY CleanTitle
HAVING COUNT(*) > 1
That'll return any duplicates by CleanTitle (where this is failing), the ids (internal for your DB), the TVDB IDs and the number of duplicates.
I did have dupes in the database. Which I did not see in the web interface. I'll clean them up. Thanks!

I had the same issue after adding "Star Wars: Clone Wars (2003)" and "Star Wars: The Clone Wars (2008)" TV series. Both had "starwarsclonewars" as "CleanTitle". I had to remove one of them for the manual import to work... Wouldn't there be a better solution here ? Adding the year to the "CleanTitle" for example (or would that be a BC break for most existing systems) ?
Most helpful comment
I had the same issue after adding "Star Wars: Clone Wars (2003)" and "Star Wars: The Clone Wars (2008)" TV series. Both had "starwarsclonewars" as "CleanTitle". I had to remove one of them for the manual import to work... Wouldn't there be a better solution here ? Adding the year to the "CleanTitle" for example (or would that be a BC break for most existing systems) ?