[Galaxy Tab Q&A, Help & Troubleshooting] shiloh12:
Well. No replies, but I did eventually solve this. Hopefully this can help someone. I am a tinkerer, but I really nearly gave up on this..But this was a cheap second hand tablet ( my first) and I want to see what it can do before I test drive one on my mother who is having nightmares with every Windows laptop I give her!

Once I got to a PC , I had access to Odin3, although it is not available online (apparently to Mac) I could not get it to work due to Java issues (JOdin3 online - brilliant idea but no joy for me so far)

I had the Rom I wanted ( GraveDigger- SMT520_GraveD_V3.0.zip ), the firmware update (T520XXUAOD2_T520BTUAOB1_BTU.zip(i think)) and the unlock file (CF-Auto-Root-picassowifi-picassowifixx-smt520.zip) , non of which I could install in any way , due to being locked out of using a custom Rom bootloader!:rolleyes:

At this point I factory reset and cleared the cache( as that is the only options in the basic bootloader!) I also has ADB on the PC so attempted to install the files this way (after messing about using some software to produce the .tar and .md5 files needed for Odin. I tried everything to get this into proper 'bootloader mode' all from scrach again, including trying the adb oem unlockbootloader command, which I would never get to work as I could not get there!

With Odin, I was also again able to flash the firmware update, eventually, and of course had to unlock again. I was curious if I could now use the OTA update, and could not. At some point, in repeating this process( as I think it hung up several times and needed a hard reboot) I had at this point fully wiped the device as I know that is another reason to have glitches and an unstable ROM later.

I think I then tried to check and although T520XXUAOD2 seems to still be the firmware, at some point I managed to get online ( I think some superuser app which I have had to try several may have notified me that KNOX was reset:laugh:When I go to About>Software update it said I had the latest update! Good news!

At this point I had installed both CWM and TWRP again , and thought I would try TWRP.I had tried CWM and the same problem, like a double flash of the Samsung Logo , so I know it had reset !!:confused:

THIS TIME I used TWRP ( I thought of trying CWM touch, but its either paid, or I would have to find and ABD the file over I guess) , I managed to re-apply the Root file, Root checker confirmed this , as it had throughout this ordeal!, although apart from ACCESS GRANTED I dont really know what the rest means..Anyway although picassowifi , was still in Device name on TWRP I chose an earlier recovery version to install.- twp-2.7.0.0-picassowifi.img. When I re-booted, I was able to get the TWRP recover image, and install the ROM, I cannot remember if I re-rooted as I was so elated.

I had a few , freezing moments, reinstalling most of my apps through Titanium Backup, I think I just tried to reinstall everything which of was unnecessary, after a hard reset, all seems fine. I checked and the TWRP recovery seems to have stuck. I am not entirely sure how to check about the firmware , but for now I feel this is progress.

Good Luck if anyone found this any use.

:D

Just to add, when you search this ( and probably many other models) you seem to get so many sites, offering exactly the same unlock information, in exactly the same way, many of the downloads seem to take you to many weird and wonderful places. So I tended to look here for downloads if possible. But I had to join SamMobile (which seems a useful site for the firmware upgrade) and trawl all over and assume similarities between other Samsung devices to fully check I was not being an idiot. But this was very odd and I could not find any posts or other workarounds that I did not try. But this new ROM feels lovely and smooth so far, and I now want to look into this tablet further