In case anyone is interested. . .here's the solution:
Go to HD > library > application support > IK > delete the amplitube 3 folder.
Go to HD > library > audio > plug ins > components and delete the amplitube3 file here
now reboot and do this. Open the HD > Applications > Utilities > Disk Utility and Repair the disk
permissions on your HD. Now reinstall the 3.8 update for AT 3 and retry it.
If anybody knows what happened initially with Logic I'd love to know!