I hope this is the right forum, as my issue spans the software/hardware categories. Three times over the last three months I've have the "Invalid Node Structure" error (MBP mid-2010). Once disk utility was able to fix it no problem. The last two times, however, (three weeks apart) I had to completely wipe my hard drive and restore from my time machine backup because the INS error seems to have been caused by a deep file system or partition issue--I think ("volume bitmap needs minor repair" was one of the things that came up when trying to repair the INS error) I did virus scans with ClamXav to see if I have inadvertently infected my system and it came back clean. Getting anxious that my hard drive was failing, I took the computer to be evaluated by certified repair peeps. They replaced the drive and I got my computer back today. When I tried to use the set-up assistant to restore my system from my backup, it didn't work. I got to the login screen after waiting two hours for my data to transfer, but it would not recognize my password (I tried several times and I know I was using the right one for the account that I was restoring--and the generic "password" and leaving it blank didn't work either). So I restarted the computer and got stuck on a blue screen upon trying to boot the system. I called the repair guy and he recommended I do a hard restart from the blue screen, reboot in repair mode, and reinstall Lion, which I did successfully. He also said that my external drive might be corrupt and that's why the set-up assistant didn't work. I desperately needed the data off that drive, however, so when I reinstalled Lion, I used Migration Assistant to move only select files (Documents, Movies, Music, Photos, and Applications) not the whole system. This appears to have worked as I can now access the data that was on the external drive. And, here's the weird part, it created two user accounts on my computer (obviously--the old one from the backup and the new one from setting up Lion clean). When I went to login to the old account my password worked! Why it didn't recognize it when using set up assistant is beyond me . . . My questions are: Is it possible that, after backing up my hard drive to the external drive, a corruption was transferred to the external drive? And after restoring my system from the external drive during the whole 'invalid node structure" fiasco, I inadvertently copied that corruption to the internal drive again--so I'm caught in this vicious circle of corruption? Also, if there is a corruption on my external drive and I copied the data (Documents, movies, music, photos, and applications) onto the new drive in my computer, will the corruption wreak havoc on my new drive? Or might the corruption be contained only to the deeper system files (which I did not restore . . .right? )? Is there any way to tell other than waiting for an INS or other disk error? Sorry if this is confusing. And thanks in advance for any advice and suggestions!