Symptoms
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Unable to update Opportunity Product by clicking on Save button. Issue is sporadic. Error occurs after clicking on Save button.
All users are affected

Workaround
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1. After updating value, clicking on Tab will update the Opportunity Product without any error
2. After updating Quantity field value, click on anywhere on Form using Mouse Pointer


Repro Steps
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1. Login to CRM 2013 SP1 UR3 Org by browsing to http://crmsql:5555/CRM
2. Click on Microsoft Dynamics CRM Tiles
3. Select Sales Area
4. Once selected Sales. Under Sales, click on Opportunities
5. On ribbon of CRM, click on '+New' button to create new Opportunity record
6. 'New Opportunity' Form will open to enter values. Enter Value for Topic as 'Test1'
7. On ribbon, click on 'Save'
8. Post saving Opportunity record, Record name will change to 'Test1'. Scroll down in Opportunity record to Tab 'Product Line Items'
9. Select Value for LookUp field 'PriceList' as 'TestPL' by clicking on Magnifying glass and look up 'TestPL' value.
10. In Product Line Items tab, below 'Revenue' Tab there is a sub grid to add Opportunity Product. Click on + sign on top right hand side corner of sub grid.
11. Post clicking on + sign, you will get two menus.
(a)Existing Product
(b)Write-in Product
12. Click on Write-in Product.
13. Under Product Name column, you will be allowed to type name just type 'Testproduct'.
14. Post entering Product Name, press tab on keyboard to enter Price Per Unit.
15. Enter Price Per Unit as '45' and click Enter.
16. Open Opportunity Product 'Testproduct' by double clicking on name. This will open Form 'New Opportunity Product' Form.
17. Under Pricing section, change the value for field 'Quantity' to '2'
18. On bottom right hand side corner, Click on Save button using mouse pointer only.
19. If error is not replicated while saving, change the value for field 'Quantity' to '3' or any value and click on Save using Mouse pointer only.

Note: Error is intermittent. We might have to repeat step#19 for about 4-5 times to replicate issue.