"Pidgin.exe was not found."

On my USB flash drive, I have the directory structure set like so:

/
    - PortableApps/
        - FirefoxPortable/
        - PidginPortable/
        - FirefoxPortable.exe (not a shortcut)
        - PidginPortable.exe (also not a shortcut)

In the above sample, I can double-click on FirefoxPortable.exe (outside of the Firefox Portable directory) and it will run.

However, when I double-click on PidginPortable.exe (also outside of the Pidgin Portable directory), I get "Pidgin.exe was not found. Please check your configuration". If I run PidginPortable.exe from it's normal location (/PortableApps/PidginPortable/PidginPortable.exe), it works fine.

I have 7 portable apps set up as above, but Pidgin Portable is the only one of them that fails to run in this configuration.

Any ideas?