When mysql5.1 is upgraded to mysql5.5, "cannot load from mysql. Proc…" appears ..."

A non-critical business m/s is upgraded from 5.1 to 5.5. after entering the console, the data dictionary cannot be queried and the following error is reported:

Cannot load from mysql. Proc. The table is probably specified upted

The solution is very simple and runsMysql_upgradeCommand. This command will generate a text file mysql_upgrade_info in the Data Directory, which contains the upgraded database version.

What makes me strange is that the upgrade has actually taken some time. When I first imported dump SQL, this error was reported and I have used mysql_upgrade to upgrade the system table, why does this problem happen again? Pay attention to this issue.