pop-up window "unknown file type " in new user desktop

[ccchen]

Hi, I'm a newbie using LXDE.
I install LXDE on arch 3.16.3-1,having a problem when adding new user.
I have searched on google and LXDE wiki, but I didn't find the answer.
After I add a new user and login, running on LXDE environment, there is a window showing "unknown file type -".
I can click "ok" to cancel it.
But each time when I type in command line/click to open a program(firefox,chrome,etc.)/click to close a program.
the window pops up again.
Intrestingly, when I click on the icon of LXDE menu on the corner/move in the menu, the window doesn't appear.

I have no idea about why it happened.
Before I logined to the newuser,
I just used "useradd" to add a new user,set the password,made home directory and add the new user to the group of other user.
So maybe I should configure something so I can run it normally...?(But I didn't have the problem when I run LXDE on the original user account)
Can someone give a cue about how to solve the problem?

Thanks for your attention on my problem!

[drooly]

you will have to do some troubleshooting to find where this message is coming from, but once you got that it should be really easy - like removing a "-" from some config file.