Follow along with the video below to see how to install our site as a web app on your home screen.
Note: This feature may not be available in some browsers.
Please try this:
Main Menu > Settings > Applications > Manage Applications > Menu Button > Filter > All > Gallery > Clear Data.

Ok that is odd that normally works. However now that you have done that please remove/reinsert the battery and memory card then let me know if there is any change.
In this case I would advise transferring all of the memory card data to a PC as a backup then formatting the SD card and transferring it back:
Main Menu > Settings > Storage > Unmount SD Card > Format SD Card (Please do not forget to back this data up first as this will delete everything on the card).

Ok one more thing, please try to update the phone by downloading and running this:
Update service - Sony Smartphones (Global UK English)