I have had the same error occur in my environment before where Jira was the ''master'' endpoint. When you create a new folder name value in the ''jirafolder'' field you need to let the QC synchronizer create this folder in QC when the sync is run. If this folder already exists (In QC) before the sync is run then the synchronizer is not able to create the new folder and give it a unique index in the synchronizer database and this results in the error.
To correct this you will need to delete any folders from the requirements module in QC that you are syncing with Jira that you created before allowing the QC synchronizer to create the folders for you. Since Jira is the ''master'' you will need to allow the synchronizer to create the folders, you won't be able to use already existing folders in QC unless the synchronizer created them.
The requirement folder is considered a requirement entity in QC and has a record in the identity map in the database. If the folder already exists in QC then the synchronizer is not able to create it and store a row in the postgres database so that it knows for future syncs that the folder has been created. This is why the error is given, the synchronizer is trying to create the folder in QC which is considered a type of Requirement entity so you receive the error in the log.
This might also be seen in syncing other requirement items other than Jira with QC, if the other endpoint other than QC is the ''master'' then this is the endpoint that the requirement folders would need to be originally created in.