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It's likely a configuration limit on your server that doesn't handle "big" operations

There is an upper limit on how much "stuff" you can do, and your webserver has a limit on how long a page can work (usually 30 sec) and how much memory it can use.

It might be that you hit one of these limits. If you have access to the log on the server, check if there is an error written when you try to do that operation... hard to be more detailed, it depends on your server and how it's configured.