10.7 ‘Internal error’, ‘Internal fault’, ‘Assertion failed’
Any error beginning with the word ‘Internal’ should never occur. If it does, there is a bug in PuTTY by definition; please see appendix B and report it to us.
Similarly, any error message starting with ‘Assertion failed’ is a bug in PuTTY. Please report it to us, and include the exact text from the error message box.