Radius tool with different curser

Hi, I’m a novice with the software so at present I’m trying to place a radius on an inside corner of a shape (merged rectangles inverted “T” shape). When I select the radius icon at left of screen and go to the corner I want radiused the curser goes to a small circle with cross hair but had RED horizontal arrows pointing left & right. What does this mean?

It should indicate that your radius is selected too large and does not fit into the selected corner. Try reducing your radius value until the symbol changes.

Hello Bernd,
I really appreciate your quick reply to my question, Yes you are right. Thr radius was set to 15mm, when I reduced it to 5mm the curser changed to the cross hair with radius symbol.
Thank you for your help,
Best wishes,