I realize this is an old thread but hopefully this reply will help someone somewhere.
During the time of CS4 an upgrade that helped fix this problem was released from Video Copilot, it’s available from the website.
Other things to try are disabling your GPU rendering (this is found under the options for your Optical Flares in File > Preferences) and deleting a preset called Evening Sun.ofp from Optical Flares Presets > Lens Flares.
I had the same issue and doing all of this corrected it. If you purchased the Optical Flares bundle, and still have problems, e-mail tech support, they got back to me even on the weekend.
Nate