Hmmm... That is weird. Might be a short in the key button. Could be something else though like a bad door switch. If you're in warranty take it in. If not you may have to anyway to find the problem.

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'05 X3 3.0i Alpine White/Gray Leather/Alum. Trim
Sport/Steptronic/Servotronic/Panoramic
Prem. Sound/Staggered 18" Style 114 Y-Spokes