Fatal error: Out of memory wp-includes/wp-db.php on line 774

Hello all,

I have a problem with memory limit after I am going to save update of site there is error message:

Fatal error: Out of memory (allocated 67108864) (tried to allocate 4407065 bytes) in /wp-includes/wp-db.php on line 774

Firstly I did re-installation of WP 3.2.1, before I deactivated all plugins.
Than I increased the limit from 80M to 128M in PHP.ini and in wp-config.php.
I install the plugin WP-Memory-Usage to check the memory limit and actual memory usage and it show:

PHP Version : 5.2.14 / 64Bit OS
Memory limit : 128 MByte
Memory usage : 36.41 MByte
Usage 28%

I have still the problem. ??
Can you help me with this?
Can be here problem with theme (Mercury)or some plugins?

Thank you for help,

Bigdrobek