Upgrading, from Mountain Lion directly to Yosemite, may require to Reset Home Folder Permissions and ACLs.
Using Time Machine I completed to migrate files from Mountain Lion powered MacBook to sparkling new one, with Yosemite.
After migration, Iguana had issues with files access permissions.
There is a hidden ‘resetpassword’ utility in Recovery Partition (boot with Cmnd+R and go to Terminal). This utility allows to “Reset Home Folder Permissions and ACLs”. Two seconds took to complete this Reset. Restarted computer; and all of my countless Iguana instances are working again 🙂