AD9851 frequency innacuracy

[Elerion]

Hello.

I'm getting trouble using the AD9851 as tracking generator.
The RSP-Spectrum Analyzer generates a lower frequency than expected.
The ratio is 2/3. If set to 10 MHz, I get 6.667 MHz.
The board is one with a 30 MHz crystal.
Software works perfect with AD9850.

Does it make any sense?
Thank you!