SQL Assistant completely disappears when user attempts to log on

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SQL Assistant completely disappears when user attempts to log on

One of my users is experiencing a problem while attempting to connect to our development environment via SQL Assistant. SQL Assistant opens up, and he clicks on the 'CONNECT' button. He then selects his datasource and the logon screen pops up. Once he enters his logon information and selects 'OKAY' the entire thing disappears... no warning, no error message, nothing.
He is able to use SQL Assistant to access the production environment with no problems.
It's not a password issue.

Any suggestions?