Vaibhav,
At one point you are saying the issue occurs when you are creating the quotation and later you say you are trying to revert the changes. Please let us know what is the situation.
Is it happening when you are creating the quotation for the first time or you have created a quotation and trying to create another one?
Best is to debug the method of the class CL_CRM_BOL_TX_MANAGER if you are interested. Also please take a look at the custom coding done in this area, specially the ON_SAVE method of the quotation where you are facing the issue.