The current fillet radius produces invalid geometry.

jonathan_starke

Once a fillet of a larger size that what you are trying to do now, is made, you get this error message

The fillet size is remembered, and you cannot create a fillet on a smaller object.

bradley_sauln

If you click and drag while performing the sketch fillet you will be able to add a smaller fillet radius if the last one was significantly larger.

Reference: https://cad.onshape.com/help/index.htm#sketch-tools-fillet.htm?Highlight=fillet

timothy_bender

This tip NEEDS to be added to the how-to tutorial and Tips for the Sketch Fillet tool. This happens quite often and finding this answer should not be this difficulty to locate.