Hi Zotteken, welcome to the Seven Forums.
First: backup in case something goes wrong!
You could try creating a link between original ProgramData and the new relocated one. Giving this command in an elevated command prompt (elevated = run as administrator) creates it:
mklink /j C:\ProgramData X:\ProgramData
(Replace X with the drive letter where your relocated ProgramData is located.)
Notice that you need to copy absolutely everything from C:\ProgramData to X:\ProgramData and then delete the original C:\ProgramData folder before using above mentioned mklink
Now try to install AVG again. If it is still not working, I do not know what else to try. An easy solution would be to replace AVG with Microsoft Security Essentials
which in my opinion is at least as good AV solution than AVG.