When launching schema browser the error Ora-00942 is returned.
User does not have permissions to the table that is being queried by Toad, in the background, to gather information to populate schema browser with.
Make sure the option "Check access to DBA views" is unchecked. It can be found by selecting View|Options|Startup.
Use SQL Tracker to capture the query being run in the background to gather the information Toad is trying to display. The SQL Tracker will capture the query and the error. You can see from the query which table/view is trying to be accessed and you need permission to. After finding the table/view, you will need to speak to your DBA to see if you can get the privilege needed.
In case you have not used SQL Tracker before here is how to:
1) Open Toad for Oracle and connect to your database.
2) Select Database | Monitor | SQL Tracker.
3) Highlight the Toad.exe line in SQL Tracker and click the start monitoring button (green arrow).
4) Go into Toad for Oracle and perform what you want to be monitored.
5) Go back to SQL Tracker to view output.
Note: It is easier to research if you start the monitoring right before you perform the action you want to monitor. That way it only captures what you want to monitor. If you click it before that, it will monitor everything and will be hard to find the output you are looking for.