An access violation error will occur when attempting to open a new SQL Editor Window while a long running query is being executed in TOAD 126.96.36.199. For example, if you have a long running query, such as "SELECT count(*) from big_table" and attempt to open a new SQL Editor Window while that query is still being processed, the error will appear.
Select View | Options | SQL Editor and UNCHECK the option to "Process statements in threads / allow queries to be cancelled."
This issue was fixed in Toad for Oracle 7.5. The latest version of Toad for Oracle can be downloaded at: http://support.quest.com/support_download/Downloads.asp.