I tried the fix on WPI.hta that is mentioned on the Bug Tracker. I am unable to install any software that has a command line parameter (such as /s or /silent). Other software installs normally. WPI just skips it and marks it with a red X.

EDIT: Problem solved. Cannot use WPI inside a directory with special characters. Moved to HDD root instead.

Thank you for you time.

Well, that's sort of a bug!
We should be able to use WPI in any location.

We will have to fix this in a forthcoming version.