This promblem has been before and appears again from time to time due to large amounts of data. The installation states that required memory is 128MB, but sometimes it's not enough. In Administration > Notifications I get error:
Fatal error: Allowed memory size of 134217728 bytes exhausted (tried to allocate 42 bytes) in C:\Development\zabbix\frontends\php\include\db.inc.php on line 672 (line number may differ every time).
Currently the problem is with request to alerts table (report4.php: 190). My alerts table is about 45MB.
I added alerts table SQL dump just in case.