Header tags SEO suddenly stopped working

[thermaren 0]

I installed the header tags SEO and got it working and all was well as recently as this morning.

 

Then I went in to make a change this afternoon, and suddenly the backend is broken: Selecting an option from the dropdown in "Page control" reloads the page but without the display of pages; changing options in "Fill tags" makes no changes happen; clicking the "test" button doesn't get me any results.

 

The oddest thing is, I have the site running locally, and it works perfectly. Re-uploading the functional files from local to webhost doesn't help fix anything.

 

This is really weird, I have no idea what could cause a breakage like this.

 

help?