This is the Properties dialog box in a Harmonic Linear Dynamic study. The units option should list cycles/sec (Hz) or radians/sec but every now and then (randomly as far as I can tell) the options disappear. When there are no options to select, the simulation will not run and gives me this error:

"Additional points are required in definition of the exciting curve, to cover the upper part of frequency range"

It does not matter if I have the simulation set up or not (i.e. materials selected, connections assigned, fixtures and loads assigned, or mesh created).

Is this a user interface issue? Or is there something else I could be doing to make these option reappear?