Why does my phone prompt me for a password (Lock Code) after I uninstalled Mail for Exchange on my device?

The password (Lock Code) protection feature is enabled during the Mail for Exchange install and remains in fact following the uninstallation of Mail for Exchange. To remove the password prompt and security features added by Mail for Exchange, a hard reset (*#7370#) of the device is required. 

Note: Take a backup without settings before reset the device. Depening on the device model, you might lose installed applications. Download and Install them again from Nokia Store.

Note: In Symbian^3 devices (e.g. Nokia N8-00, E7-00, E6-00, X7-00, C6-01... ) the internal mass memory E: will be formatted in this situation. It is therefore important that you back up all your data (also pictures) from the E: mass memory before resetting the device. Use Nokia Ovi Suite to back up the contents to your PC.