Logged in, got error:

Bug #1
1x Error loading PetTracker\Libs\Sushi-3.0\Classes\Dropdown.lua

Bug#2
1x Error loading PetTracker\Libs\Sushi-3.0\Classes\TabGroup.lua

Bug #3
1x Error loading PetTracker\Libs\Sushi-3.0\Classes\FauxScrollGroup.lua

Bug #4
1x Error loading PetTracker\Libs\Sushi-3.0\Classes\IconCheck.lua

Bug #5
1x Error loading PetTracker\Libs\Sushi-3.0\Classes\ExpandCheck.lua

Bug #6
1x Error loading PetTracker\Libs\Sushi-3.0\Classes\ColorPicker.lua

Bug #7
1x Error loading PetTracker\Libs\Sushi-3.0\Classes\TextureButton.lua

Bug #8
1x Error loading PetTracker\Libs\Sushi-3.0\Classes\TabButtons.lua

Bug #9
1x Error loading PetTracker\Libs\Sushi-3.0\Classes\HelpButton.lua

Bug #10
1x Error loading PetTracker\Libs\Sushi-3.0\Classes\GrayButton.lua

Bug #11
4x Error loading PetTracker\Core\Compare.lua

In addition to the 11 errors listed above, I am getting the following as well:

Bug #12
Error loading Interface\AddOns\PetTracker\Libs\Sushi-3.0\Classes\TextureDropdown.lua

Bug #13
Error loading Interface\AddOns\PetTracker\Libs\Sushi-3.0\Classes\Slider.lua

This is with only PetTracker loaded, no other addons. I also made certain it was a fresh install, with no older files or variables left over from previous versions.

This seems to get (mostly) fixed by manually installing the Sushi-3.0 and Poncho-1.0 libraries found on this site.

Once the libraries were updated, I started getting only one error message -- Bug #11 from above:

Error loading Interface\AddOns\PetTracker\Core\Compare.lua

I hope this helps. Looking forward to using this addon again :)

D.