Internal Error #1

[Pfsunmin]

I was trying to make a new collection page https://imslp.org/wiki/Mazurkas_(Chopin ... %C3%A9ric), which was originally redirecting to another collection page https://imslp.org/wiki/Mazurkas,_IFC_12 ... %C3%A9ric).
I made a new collection page by editing the document, however, after that, I couldn't upload a new file to the page with an Internal Error #1 message.
How can I solve this problem?

[Sallen112]

Try uploading a file now.

[Pfsunmin]

Now it works! I didn't know that the FILE thing was missing on the page.
Thank you so much!