It looks like you ran that version check SQL in SQL*Plus. Will you please run it in Toad so we can be 100% certain that you are connected to the same database that gives the schema browser error?
The only other thing that I can think of is that maybe you have the query set by a filter. If this button does not look grey like it does in my screen shot, then click the dropdown next to it and then "clear filter for tables"
