Check the number of turns parameter. This must be an integer.
And of course, you should not make
everything optimizable. To control inductance value, you can tweak
one dimension (overall length or overall width) of the coil, or for larger changes you can tweak the number of turns in steps of 1 turn (integer).
Also note that the geometry must be "possible" to draw, if you optimize all parameters independently
you will run into combinations that are not physically possible (impossible to draw) . In my Inductor Toolkit for ADS, there is a pre-calculation of inductance based on equations like this:
and then one single parameter (coil diameter) is tweaked to reach the target inductance, with all other parameters constant.
My advice is: use your brain and the calculator linked above to pre-calculate meaningful parameters (dimensions), and then optimize one parameter in ADS to reach the target.