Getting around the fillet tool only working once!

I use the fillet/chamfer/scallop tool on shapes you can do it once then wont let you do it again?

Here's a cool thing in addition to what Chris said:
Move the cursor to the area between the up and down arrows next to the Radius box.
You will notice how the cursor changes to arrows with a line in between.
Click and drag up- or downwards and you can see a live preview of the corner roundness as you drag.

thank you... It was a shape already done and customer wanted to make it more filleted. I have worked a way round thanks for the extra tips though!

Don't know what method you used to return to a sharp corner but here's a tip that might be handy:

1. Select the object with the Shape tool.
2. Click on the curved segment you want to remove and Delete it.
3. Select the two end nodes.
4. From the Join Curves docker, select Extend mode and increase the Gap tolerance to a suitable distance and hit Apply.

This should "recreate" the original sharp corner, ready to be filleted again.

Bonus tip: You can create a new filleted corner without going back to the F/S/C docker.
Skip step 4 above and select Fillet mode instead of Extend and play with the radius setting.
This will create a filleted corner without doing it sharp first.