I was getting this error message when my alternator starting active finicky. I monitored it and sure enough occasionally the voltage would drop from 13.5 to 11v while driving and immediately after the Self Level Inactive message would come up. It happened every few days. I finally replaced the alternator and it hasn't happened again. Try monitoring your voltage while you drive around with the OBC set to show Volts.

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Current Bimmer
2004 X5 4.4i Sterling Grey Sport/Premium

Past Bimmers
1991 318I Alpine White
1995 740I Alpine White
1991 525I Schwartz
1998 323IS Scwartz
2004 330CI Cabrio Titanium Silver Metallic
1995 540I Schwartz
2000 Z4 3.0 Titanium Silver
2000 330ci Coupe Titanium Silver