While running apper to install downloaded software I had a power failure. Before that apper worked just fine, but now it always fails to install anything.

I get an error message that says "A problem that we were not expecting has occurred."
In the details section it says this:
[PK_TMP_DIR|dir:///var/tmp/TmpDir.S40Win] Repository already exists.
An ls listing shows no directory named TmpDir.S40Win in /var/tmp, and every time I try to run apper that directory name is different in the error details.

How can this be fixed so I can resume using apper to install software?