It's complicated, because it depends on the admin user being a member of the Administrator User Group, the Policy attached to the Context Access ACL entry giving that group access to the mgr context, the role of the admin user in that group, and the specific permissions granted in the Policy. Most of the relevant values would be numbers or complex JSON strings rather than names and they're scattered among a half-dozen different tables.
TBH, I think the simplest method would be to upgrade to 2.2.1, then go into the modx_users table and put a one in the sudo field for yourself. Then delete all the files in the core/cache directory and clear your browser cache and cookies before logging in.
That should let you fix things based on the default values in the link I gave above.
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PLEASE, PLEASE specify the version of MODX you are using.
MODX info for everyone:
http://bobsguides.com/modx.html