The frequency values are read from the file ds.frq (located in the "modelname.ds_data\design scenario #" folder). I think chances are good that there is something wrong in that file. You can open it with Notepad and see if the contents are okay. If there is something different, you may be able to correct it.
The ds.frq file created on my computer looks like this:
Frequencies = 5
mode circular
number frequency frequency period
(rad/sec) (Hertz) (sec)
------ ----------- --------- ------
1 1.4935E+01 2.3769E+00 4.2071E-01
2 6.6342E+01 1.0559E+01 9.4709E-02
3 9.1572E+01 1.4574E+01 6.8615E-02
4 1.0836E+02 1.7246E+01 5.7983E-02
5 1.3112E+02 2.0868E+01 4.7920E-02
John Holtz, P.E. Global Product Support
Autodesk, Inc. If not provided already, be sure to indicate the version of Inventor Nastran you are using!"The knowledge you seek is at knowledge.autodesk.com" - Confucius 😉