Hard to tell, here are a few generic things:
- make sure your mount is balanced and the mount doesn't feel too loose when you try to move it by hand in the RA and DEC directions.
- it should "sound reasonable" when you slew both motors
- no large cable drags,
- calibrate a bit more aggressively, that is, use something like 10 iterations and 1000ms pulses (it will stop at about a 20 pixel deflection, and thus not likely use all 10 iterations)
- use the SEP MultiStar guiding algorithm
- Guiding doesn't work well very close to the pole. Are you very close to it?
- Have a look at the little calibration summary page (see image below) in the guider options menu--are RA and DEC pretty close to orthogonal? What values are you getting for pulse ms/arcsec?
- I personally calibrate once carefully, make sure it's good, and re-use it for months (using the recommendations of the PHD2 folks, e.g. calibrate near the meridian and equator). However, clearly you should first get things working well with calibration before trying that.
- report back with a log.

Also, if these don't help, you might also try using PHD2 and running their diagnostics.

Hope this helps,
Hy