My 2 cent for dojo not defined:
Application works on development-machine #1 and not on production-machine #2 with the same browser: Often an issue of different domains. The JS-API has to be configured with FQDN, the application also. Test it with a simple client to get to know if it's an application issue or a system-environment issue.
Application works on browser #1 but not on IE: Often a problem of the application code. Missing commas, semicolons, forgotten var declarations. Firefox walks over this issues, IE doesn't. Strip down the application, comment functionality to get to know where and when the error occurs.
HTH.