Thanks for your replies!
After writing topic "buffer pool is too full..." the error message is never appeared again... (before it appeared 3-5 times per day)
What I have done last (sorry, I've forgotten to write it before):
I had refreshed my bookmark.nsf and personal address book with original IBM templates and renamed the template name to Bookmarks9 and StdR9PersonalAddressBook respectively (to prohibit refresh on server over night).
Background: Based on the fact, that my home mail server is still on 8.5.x, my roaming servers is the same server, I had the idea that the source of the problem could be the mix of R8.5 design on server and R9.0 design on local considering also the design update task over night on server.
Anyway If error message reappears I will post the results according reply recommendations.
Notes:
a. I checked the notes.ini several times, nothing special found - anyway I checked the notes.ini now again and suppose notes.ini entry TemplateSetup=900000 was another value on 3rd. April (something with 8...)
b. As I wrote I had no crash till now after error message