We have released a bug fix release of the J!MailAlerts core user plugin to fix an issue which led to an error every time the Store User joomla function was run. This led to errors while saving the Joomla or JomSocial profile for instance..
This issue has now been fixed in the version 1.01 which you can download here : http://techjoomla.com/jmailalerts-core-user-plugin/view-category.html