Without information on your X as pre-facelift or facelift, it's hard to chime in.
As StephenVA posted, it could be the AE bulb if you have facelift X. I think the reason that AE shows up as side light is because of the LCM. Our X5 was based on the E39. In facelift E39, the AE bulb also power the tiny corner light (or side light), and monitored by the LCM. The X5 shares the same LCM. The corner light on the X5 is referred to as "parking light" in NCSExpert, but the message displayed from the LCM to the cluster is still "side light"
For pre-facelift, I would atleast remove the bulb for visual inspection.

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00 E39 DINAN S1 //M5 (82k miles)
06 E53 DINAN 4.8iS, born 2/18/2006 (126k miles) http://www.xoutpost.com/bmw-sav-foru...s-my-dslr.html
90 Straman Z32 TwinTurbo Convertible, (1 of 44 ever made) 5 speed, 444rwhp/451rwtq
01 360 Novitec Spider F1 (26k miles)