How are you trying to enter test mode? With sd card and testmode.key or by button presses?
Try pulling radio fuse or power (both yellow and red wires) for 10 minutes or so.
I trying all of testmodes: 104bytes, 164bytes, 132bytes - the same resault.
Cards was 2Gb, 4Gb and 16Gb, formatetd with fat32 and fat - the same.
Device unplugged, and stay alone on the table 
So, I have full backup previosly state of device - NAND& NAND2, but how I can go to filemanager...
Pressing to buttons (Home+ then 3xback-forvard) - not working.
After upgrade all will be Ok, and testmodes was worked, but may be I delete same files from NAND...
Here little video of curren state http://sendfile.su/757813
May be you know another methods, such as formating flash, or have another files to lay on SD (for example as described in service manual: How to Start-up Test Mode
1. Download GGS1098 from the Service Site.
2. Decompress the file.
3. Copy the decompressed file to the SD card root.
4. Insert the SD card to the product and turn ACC on )?