Nav-sql slow perfomance + WM + Citrix

denvio

Hi
We have WM(win 2003 sp2 4Gb). User connects to nav(3.7) client(on this wm machine) in citrix.
Nav Client connects to SQL DB(2008 R2) on another server. Everyting is good. But in hour of intensive work we have a picture: nav starts "exec dbo.Proc....." and it hanging...
no sql activity... it may hangs 20-40 min and then sql procedure starts and executed successfully. And so on any sql query from nav. If we connect direct nav link not citrix from user machine during this hang - everythig is working fine. We also have another WM+citrix on another server and it also working fine during the hanging first WM.
If we restart WM - everyting is good again first 1-2 hours.

Tell me pls what to look into