every time i try to refresh my application manager , an error message will come up that it is unable to refresh package. and it is pissing me off.
is there any way that i can fix this problem?

What that always means for me is that the last thing I tried to install failed. So I go into Tools and Application Catalog and scroll down to the end of the catalog list, highlight the last item and delete it. Then I can refresh.

go to Tools->Log... in the Application Manager. This will show the repository to which it is objecting. Sometimes it's when I mistype, other times repositories stop being available. As mentioned above, frequently it's the last repository I added. I delete it and refresh works again.

thank you, now it had refreshed perfectly. Now i am happy!