User receives "Access Violation at address 00000000. Read of address 00000000" error when connecting to a database using a 10g client.
Multiple Oracle 10g clients.
When encountering Access Violation errors when connecting to a database, ensure that the Oracle Home that's being selected in Toad, is also first in the Windows Path variable if there are multiple Oracle Homes on the client PC.
Modify Windows Path variable and remove all 10g client paths, except for the client path that is used in Toad. Ensure this path is the first path located in the list of paths.
It is also possible that this problem appears just after upgrading Oracle Designer for example.
If Help | Support Bundle | Oracle Homes Data indicates that an Instant Client is installed, this must be the first entry in the Windows Path variable.