The indexer can handle a million urls no problem, so its not quantity, but its most likley data in the list thats causing the issue.
Try pasting the list into notepad and then saving it and then opening it in rapid indexer.
OR I guess I should ask how many indexer services you have? Because it multiplies the urls to index by the indexer services and if that turns out to be a ultra massive number that could cause a grid failure.
Try loading in 10K urls from your list instead of 52K, does it do this?
If it works, try lowering the number of inedexer services.