Narrative:

On climb with vectors I believed I was to climb to 7000 ft. When ascending through 6700 ft MSL I was told I was cleared to 6000 ft only. I immediately descended to 6000 ft. I was told I was not in conflict with other traffic. I then was issued higher and continued with the flight.

Google
 

Original NASA ASRS Text

Title: PLT OF A SOCATA TBM700 OVERSHOT ASSIGNED ALT DURING DEP CLB RESULTING IN DEP CTLR ALERT AND RETURN TO ASSIGNED ALT.

Narrative: ON CLB WITH VECTORS I BELIEVED I WAS TO CLB TO 7000 FT. WHEN ASCENDING THROUGH 6700 FT MSL I WAS TOLD I WAS CLRED TO 6000 FT ONLY. I IMMEDIATELY DSNDED TO 6000 FT. I WAS TOLD I WAS NOT IN CONFLICT WITH OTHER TFC. I THEN WAS ISSUED HIGHER AND CONTINUED WITH THE FLT.

Data retrieved from NASA's ASRS site as of July 2007 and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.