If you're using 5.5, try this:

From the Windows Client, choose Tools - Reports and then click on the Mange Reports button.
Find the report you want (but can't see) in the Web Client and click on Edit.
On the Security tab, near the bottom, under "Accessible from" - make sure that the "Display in the Web Client" box is checked, and that the "Don't show this to users yet. (Inactive)" box is unchecked.

I'm pretty sure that 5.6 is close to the same screens/choices, but maybe someone else can back me up on that.