Trouble resetting lamp hours on Studio Spot 575

I've been having a # of issues with two Studio Spots. Just as I get one resolved, another occurs.

The current problem involves the lamps lamping off after about 15 minutes of use. They can sit idle, but once they go into action, they start to lamp off. Lamps were just changed a month ago. I've been told that sometimes the lamp hours not being reset can cause the lamps to shut of as a precaution against damage. However, I've followed the manual instructions for resetting the lamp hours and no luck. I've held down the enter button for as long as five minutes.

Any solutions to this problem?

Please note that I am not getting any heat related error messages.
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