If you are having an issue whereby you are updating a product or member details and it's not saving the changes then there are usually two main reasons for this:
1.) You recently updated the plugin and did not follow the instructions :)
You must deactivate and reactivate the plugin after you update it.
eStore Installation and Upgrade instructions - http://www.tipsandtricks-hq.com/ecommerce/?p=31
2.) There are some plugins that do not play nice with other plugins and prevents you from being able to save changes via the Admin Panel. You can read more about these plugins here:
http://www.tipsandtricks-hq.com/forum/topic/list-of-plugins-that-dont-play-nice-conflicting-plugins
The following link will explain how to test if you are having a plugin or theme conflict:
http://www.tipsandtricks-hq.com/forum/topic/test-to-identy-a-conflicting-theme-or-plugin
If you are still having an issue please let us know and we will take a closer look at this for you.