"The iTunes library file cannot be saved. A folder was specified instead of a file." ...what? I just updated to iTunes 11.

Now I get this error:


Huh? Some Googling turns up people with this problem in iTunes 7 &amp; 8. That was a while ago. They suggested various things, including rebuilding the library (which I am NOT going to do unless it's the only option).

However, my search prompted me to look in my iTunes folder. Yikes:

Most of those temp files appeared on 11/18/12, so this must have been happening before today when I upgraded.

So, is there a good solution? Why might this happen? Is re-building the library the only way? I'd rather not lose my date-added and play-count data.
This is a possible solution that I came across and (initially) it seems to have worked for me:

Quoted from Apple Support Communities:


  I assume the problem is gone now and here's what I did to get rid of it:
  
  
  stop iTunes
  alt-start iTunes, so it offers 'Create Library' and 'Choose Library'
  choose 'Create Library' to create a new library (iTunes 1)
  stop iTunes
  alt-start iTunes, so it offers 'Create Library' and 'Choose Library'
  choose 'Choose Library' and chose my main library, which caused me so much pain 
  
  
  since then no more tmp files are left over in the iTunes folder and I hope it stays like this