Entity too large error when uploading to XLSForm

Welcome to the forum, @Amit_Kohli! When you get a chance, please introduce yourself here. I'd also encourage you to add a real picture as your avatar because it helps build community!

It sounds like XLSForm Offline works, but pyxform (what you call python autoconverter) isn't working? What versions of both are you using?

I think XLSForm Online (http://opendatakit.org/xlsform) is failing because the web server doesn't expect files that big. That isn't really a bug with the converter, but more an issue of the server's configuration. If you OK sharing your form publicly, please upload it to this topic so I can test it against the server and make adjustments.

And as an aside, 50,000 selects is a lot! I don't know if you are using Collect to render these, but there are a couple of ways to make these more performant. One is external selects and the other is search(). We are also working on an optimization that will make big lists of selects load very quickly (in our test case it's gone from 13 seconds to 1 second).