Why SysID sometimes lost after changes in project?

Hi all.

Sorry for my bad english %)

I have a question.

Sometimes, when i change a SOPC project (e.g. add some standart IP's), after compilation NIOS EDS does not see SysID (it not found on target base address). Trying to regenerate SOPC, recompile project will not help.

Also, this situation repeat if i try to insert my own changes into standart examples.

Anybody know reasons ot this situations?

Thanks to all!

P.S.: CIII120 dev kit.