You do not have 2 different attributes mapped to the same extended1 column (for example, the same extendedNumber=“1” property on 2 different tags)
You do not have one attribute mapped to more than 1 extended1 column (for example, the same repeated, each with the same extendedNumber=“1” property, or one with 2 extendedNumber properties)
You do not have one attribute mapped to an extended1 column and also mapped to a named column (for example, the same with extendedNumber=“1” and namedColumn=“true” properties)
Also make sure the .hbm.xml doesn’t have similar issues. When you go to Global Settings > Identity Mappings and click Save, this automatically maps each attribute to the next available extended attribute as defined in your .hbm.xml file, so that most likely fixed your issue
Also sometime this is false error , you click on Attribute mapped extended1 and then click on save , may be this error will be gone .
This resolved my issue. I was using 2 tags: extendedNumber=“1” and name=“extended1”.
Also, had some unused attributes in the*.hbm.xml. Commented the entries.