W810 Unlock Problem ("Configuration Error") solved

Flashed my phone using SeTools Lite 1.11 and using Firmware from Top Sony - All about Sony Ericsson mobile phones. Free Firmware Download - Unlock - Upgrade - Debrand. There are all relevant instructions on Topsony somewhere. However after flashing and patching my firmware got the message "Configuration error. Contact..." when using a T-Mobile SIM card. Thought the patch had not worked and got quite frustrated, but it is true - you need to apply customization settings to resolve this problem e.g. download a customization .zip from Top Sony - All about Sony Ericsson mobile phones. Free Firmware Download - Unlock - Upgrade - Debrand and choose it under MISC files in SeTool2 (After having flashed the main, FS and patch beforehand). Make sure you link to the .zip file and watch the status window which should say "FILE RECOGNIZED AS CUSTOMIZATION PACKAGE."

Then press flash and voila - it worked for me!