First place to look if you have not already is the browser automation information the product help.
Browser applications can sometimes be a bit fiddley to interface with because they often have multiple application process threads as part of the one application. It might be worth experimenting with something along the lines of - launch application, wait for window, disconnect from application, reattach to application - that can sometimes help. If you get your error during wait for window you can do the wait using the environment utility instead. Another thing to try might be to launch via command line, use environment utility wait for process window, then attach.
Attaching to the browser application post-launch can make sure you are correctly attached to the correct process thread, as sometimes things can get in a twist during normal launching.
