I recently heard from a user who said that it wasn't possible to filter the contents of the problems view, and realized that others may also not realize that this is configurable. If you click on the little arrow that is on the far right on the problems view's title bar, you get a drop down menu. If you choose "Configure contents" a dialog is shown, pictured below.
If you check off one or both of errors and warnings, and then for the Scope setting, choose "On any element in same project," the problems view will only show the errors and/or warnings that apply to the selected project. This is just standard Eclipse function, but is built right in to Domino Designer.
And of course another way to filter the errors out would be to just fix them :-)