Error while saving a model

Hi,

I'm facing an issue when I try to save a model(Please refer below image).Before saving the model I performed below steps:

1)Opened an existing model of any model type(for example :Knowledge Structure Diagram model type)

2)Now I copied the already existing object(specifically of Documented Knowledge object type) in the model and pasted it as "Definition Copy" in the same model.

3)There is no problem in pasting the object,however when I now try to save the model, I get the below error.

Could anyone please guide me what can be the exact reason for this issue.

I tried DB Optimization as well, but still this issue is getting replicated.

Can someone please help me with resolving this issue

Regards,

Krishna Boddu