In the transition from 4.18SP3 to 4.19 Atmel made a change to AVR Studio so that it would no longer automatically look for WinAVR. Yet many people still want to use 4.19 and WinAVR20100110 together.
If you have installed the two programs and then create a GCC project in 4.19 and try to build you will get errors about it not being able to find the tools.
To correct this, for each GCC project you now create use "Configuration Options" on the Project menu.
In the dialog that appears switch the 5th/final tab "Custom Options"
In the External Tools box untick (if ticked) the "Use AVr Toolchain" box.
In the avr-gcc: box below set the path to be C:\WinAVR20100110\bin\avr-gcc.exe (adjusting drive and pathname if you installed in a different location - use the file browser button there if you are not sure of the location).
In the make: box set it to be C:\WinAVR20100110\utils\bin\make.exe
Click the [OK] button.
Now try to build again and it should work.