increments of 1000, 100, or 10 problems

This happens on add-on planes, sometimes using default planes. I can only dial in ALT. in increments of 1000ft, speed and heading in increments of tens. Any Ideas?
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Great call Arthur!
Dont have a FSUIPC to 'open', just the dll in FS2002/modules, but opened 'fsuipc.ini', also in the module folder, and found the line 'fixcontrolaccel=no'.
Changed to 'yes' and the 737 ap appears back to normal.
Thanks
Cheers,
Dave