My b2evolution Version: 1.9.x

I am trying to write an expert post and get the following error:

Fatal error: Allowed memory size of 18874368 bytes exhausted (tried to allocate 38 bytes) in /hermes/web09/b838/pow.moskomarsh/htdocs/blog/inc/MODEL/users/_user.class.php on line 127

This happens on 3 of my 5 blogs. It does not happen when trying to write a simple post.

http://heartlightcenter.com/blog/index.php/b

Is this a problem with my powweb host or with my installation of b2evolution? Do I need to upgrade from v1.9.3?

Please let me know what other info I need to provide.

Thanks in advance.

Marsha