Getting exception error after creating the new version of the Quote

Hi Team,

Here I am facing an exception error after I created the new version of the Quote, to brief you, I fist created the new version and its created successfully. I created new version because my approver rejected my approval request. However, after creating the new version I did some changes on the Quote lines and try to save. As soon as I save system showed an error, attached is the exception stack of the error please review.

However, when I tried to understand an error and changed the start and end date little bit for the new version of the quote and save, then system accepted. And I was able to save the "new version" of the quote and able to re send to the approvers after creating the new proposal documents.