I used to get that and I found out it was the main battery, issues went away after the replacement. By the way cruise control does not work when you have the warning is showing on the dash.

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06 MB E320 CDI 123k miles
14 Sienna (wife's DD) 36k miles
11 GL350 Bluetec 136k (Sold)
96 E300; 292k+ miles (Donated)
11 Sprinter 22K+ miles (Sold)