The troublemaker:
NEVER EDIT ACCOUNTS IN MULTIPLE TABS!
If you do, you'll probably loose all admin rights for all accounts (like I did).
The solution:
- Open "Database Manager"
- Expand "NetPerfMon"
- Right-click "Accounts", choose "Query table ..."
- Click "Execute query", then "Enable table editing"
- Scroll to column "AllowAdmin"
- Change value from "N" to "Y" for your admin-account.
- Click "Enable table editing" again.
- Close "Database Manager".
- Log in to/refresh web console.