Toad gives the error "Access Violation at address 6761D581 in module 'ORA805.dll'. Read of address 00000010" when doing a Session | Test Connection (Reconnect). Connected using Oracle client 8.0.5.
Please upgrade your Oracle client to match the Oracle Database version.
In Toad for Oracle 10.0 and up, the client support is limited to Oracle v8i Client Net 8, so only version 8.1.7 and up. Clients like 8.0.6 or older are not supported and will give the access violation regardless of server version.