S4 SCH-i545 Odin "FAIL! (Auth)" Error: Downgrade

Here's my problem: I recently changed carriers from Verizon to T-Mobile. After my first week on T-mobile, I realized that I couldn't send texts. After dealing with the tech support on T-mobile's side, they told me that there was nothing they could do. After doing some digging of my own, I realized that right before I changed carriers on Verizon, I updated my firmare to Lollipop, which is not yet available for T-mobile. I though this could be the reason why my phone could not text. So currently I'm trying to downgrade my phone using Odin, the Kit Kat firware from Sammobile, amd the samsung drivers. It keeps failing though. I don't understand why. This is the log I keep getting:

<ID:0/004> Added!!
<ID:0/004> Removed!!
<ID:0/005> Added!!
<OSM> Enter CS for MD5..
<OSM> Check MD5.. Do not unplug the cable..
<OSM> Please wait..
<OSM> I545VRUFNK1_I545VZWFNK1_I545VRUFNK1_HOME.tar.md5 is valid.
<OSM> Checking MD5 finished Sucessfully..
<OSM> Leave CS..
<ID:0/005> Odin v.3 engine (ID:5)..
<ID:0/005> File analysis..
<ID:0/005> SetupConnection..
<ID:0/005> Initialzation..
<ID:0/005> Get PIT for mapping..
<ID:0/005> Firmware update start..
<ID:0/005> SingleDownload.
<ID:0/005> aboot.mbn
<ID:0/005> NAND Write Start!!
<ID:0/005> FAIL! (Auth)
<ID:0/005>
<ID:0/005> Complete(Write) operation failed.
<OSM> All threads completed. (succeed 0 / failed 1)
:crying:
And yes, I have USB debugging on, cleared my cache, and allowed downloading from unknown sources...
If anyone could think of ANY reason why it's not working, PLEASE tell me. :highfive: I wouldn't be here if I wasn't desperate. :eek: