"Notes error: Unable to write to database because database would exceed its disk quota."
Even after the quota is reached, you are still able to copy, paste, and add documents to the database.
Solution
This issue was reported to Quality Engineering as SPR# GMAA64MK4R and was fixed in Notes release 6.5.5. Now, if you set the parameter, REPL_OBEY_QUOTAS=1, in the notes.ini file, archiving will NOT be performed if the database is over quota (although you may not see the quota error all the time).