I'm trying to create a forming tool for sheet metal but there is an error if I bottom fillet.

The error is

The part's thickness may not be compatible with this form tool. The thickness must be less than the minimum radius of curvature for the form tool.

But if I suppress the bottom fillet, the error goes away. Also there is prebuilt forming tool, that is very similar and is working just fine.

Where could be the problem ?

Thank you.