TortoiseMerge "not found" error for newly-added and deleted files

By mail.sm... on January 09, 2011 19:00 (imported from Google Code)

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What steps will reproduce the problem?

1. add a file to the repository (or delete one)
2. open the commit dialog
3. double-click the added/deleted file

What is the expected output? What do you see instead?

Expected: TortoiseMerge opens, displaying the contents of the file in the right tab
Actual result:
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TortoiseMerge
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The diffing engine aborted because of an error:
Can't open file 'C:\Users[user]\AppData\Local\Temp[filename]': The system cannot find the file specified.

What version of the product are you using? On what operating system?
1.6.2.0
Win7 Professional x64 (fully patched)

Please provide any additional information below.
Issue #77 (closed) is similar to this, but it has been fixed over a year ago. Looks like the problem reappeared.