Chris,

   I am also puzzled why this is happening every 3-4 days. Base table is modified every hour. I think SQL Server is forcing recompilation of all procedures referencing base,mail, table when certain threshold of modifications reached and it beleives statistics is out of date. Would you agree?

   When [COMPILE] locks were generated, there was no plan cached for this proc in syscachobjects. I issued sp_recompile vsp_mail_select. This seemed to help (I am not 100% sure though). After sp_recompile, I started seeing Compiled and Executable plans in syscaheobjects for this proc. Assuming changes in the base table is the reason for recompiling, what course of actions would you recommend?

Thanks,

Igor