Hello guys. I was trying to open the Software Manager using the following path (on xfce):

menu -> settings -> settings manager -> install/remove software

It started loading normally but then the following error message appeared:

The following packages have not been found on the medium %F
And after displaying the message it quits. After that I tried this other route: menu -> settings -> install/remove software. Using this last path the software manager opened with no problem.
I would like to know why is the error message displayed and if I should do something to fix it.

Thank you for your help.