Excel non responsive

I have an datavalidation control in a worksheet. I have written code( includes formulas) for populating certain cells on the worksheet change event. When I select 'Yes' from list then cells should be populated and when I select 'No' cells(including formula) should be cleared. Some of the cells contain formulas which are calculated using an Add-In. When I select Yes to No or No to Yes, 'calculate' is being displayed in the status bar and excel become non responsive. If I handle the functionality in the click event (for example I used option button click event) then it works fine. Still if I select other validation controls, excel starts showing 'calculate' in the status bar and subsequently hangs. If I close the application then it displays error message saying 'Microsoft Office has encountered a problem and needs to close'. These list controls are populated using another ranges.

Could you please suggest what can be the reason why Excel becomes un-responsive?

I am disabling the events. Actually Application interacts with a third party Add-In. When I do a specific action using this Add-In, it will insert formulas to almost 36 cells. If the cells doesn't contain any of these formula then application works fine. All other functionalities like radio button events are working fine. When ever I select any value from any data validation controls for which a cell change statement is written, then application shows 'calculate' and hangs subsequently.