I had the same problem, but I fixed it another way. It's not for the faint of heart though.
I had tracked the problem to the Product Code, it had somehow become invalid. The Product Code is set in file /efs/nv_data.bin, and I think Kies reads it from the file, and compares it to the Product Code of the ROM. If they don't match, Kies won't let you upgrade. In my case the code had to be damaged, as Kies was claiming my code was ÿÿÿ.
I checked nv_data.bin and it looked like it had indeed become damaged somehow, as it wasn't 2048 KB, as it's supposed to be, but 2049 KB. The backup .nv_data.bak was was in better shape, I made it the main file, but that didn't work. It too was damaged. The Product Code is set at offset 0x188000. It looked like this:
Code:
FF FF FF FF 4D 50 20 31 2E 32 30 30 00 00 FF FF ....MP 1.200....
FF FF FF FF FF FF 47 54 2D 50 31 30 30 30 43 57 ......GT-P1000CW
41 50 48 4E 00 00 00 00 00 00 01 50 02 4E 03 4E APHN.......P.N.N
That's not correct, I know from other people's posts of their Product Codes it should look more like this:
Code:
FF FF FF FF 4D 50 20 31 2E 32 30 30 00 00 FF 50 ....MP 1.200...P
48 4E 00 00 00 00 47 54 2D 50 31 30 30 30 43 57 HN....GT-P1000CW
41 50 48 4E 00 00 00 00 00 00 01 50 02 4E 03 4E APHN.......P.N.N
Note the extra code PHN that should have been there but somehow had been overwritten by 0xFF. That explains the odd code in Kies as 0xFF in ASCII is 'ÿ'. I then edited nv_data.bin in a hex editor on my PC to look like the above, and flashed a Froyo ROM I had found on sammobile.com which luckily had a CSC with the correct code PHN. Unfortunately most ROM's from sammobile don't include the necessary CSC, and neither do the files you can download with fus.nanzen.se.
I finally connected the Tab to the PC, and what do you know, Kies recognised the Tab immediately and updated it to GB 2.3.6 successfully!
---------- Post added at 12:28 AM ---------- Previous post was at 12:13 AM ----------
To find it you have to remove the space from the link.
It's an app that can fix certain problems with DHCP by releasing and renewing the lease.