You are not able to delete an old instance from the Capacity Manager for SQL Server Repository. When you try to press the "delete instance" button from the repository node you get the following error message.
The DELETE statement conflicted with the REFERENCE constraint "qcm_FK_partitionsize_partitions". The conflict occurred in database 'QuestSoftware", table "dbo.qcm_partitionsize", column 'partitionid'.
WORKAROUND:
In the Capacity Manager console click on the Repository node and Find and Delete all Snapshots related to the Instance you want to be dropped.
After that the Instance deletion should be completed successfully.