How do I fix Allowed memory size exhausted error?

The problem may be related to the amount of RAM that the scripts need.
The full message may look like this:

Fatal error: Allowed memory size of 64M bytes exhausted

By default, the limit is set to 64M. The set value can be changed by adding the following line to the .htaccess file, where the value of 128M is the amount of RAM that can be (for different packages the maximum values are different) maximum allocated for the script:

php_value memory_limit 128M

This is, of course, one of the many parameters you can use. More information on this topic can be found HERE.