Simple Tags By Amaury Balmer was the culprit in crashing my blog on Save. Whenever I tried to save anything, I used to see blank page on Admin side after update to WordPress version 3.2.1. Simple tags plugin is for
adding Extended Tagging for WordPress 3.1 : Suggested Tags, Mass edit tags, Auto-tags, Autocompletion, Related Posts etc. NOW Compatible custom post type and custom taxonomy !
Possibly this plugin is not required now, as I see by default WordPress is auto-completing the tags already used. There were other features but those features needed very rarely.
What to do when you see blank page on Admin side or any error on Admin side?
First of all try to use this in wp-config.php file.
More details on WP_DEBUG.
If this does not give you definite clue other than few 'Notice' Error, then you can go through the process I went through. Plugins you are using can create problem. Try to deactivate all plugins. Select all plugins and using drop-down menu deactivate all WordPress plugins at a time. Do whatever you were trying to do and see if are still seeing those problem! If not then one of the plugins you were using were creating the problem.
Now, the solution is trial and error method.
Select plugins one-by-one and activate them. Start from most trusted and most important one so that if you are in hurry for some other work you can go with important plugins running.
After each set of plugins activation, do the same job were you saw problem. If problem is not coming then all plugins you selected till now is working fine. Continue with this job until you see the problem has come back. If the problem has come back then the most recent activated plugin is the plugin caused to crash your WordPress PHP script. Discontinue using them and inform to plugin author about the issue. This will help the plugin author solve the issue. On wordpress.org plugin page, on right side, there is place to tell about wroken plugin version and wordpress version.