We have improved the error response your get when you hit an Error against Dynamic CRM with Data Sync. We now format the request in a more human readable format and add this to the Error Log along with the response from Dynamics CRM.
For example attempting to Update the total amount on an opportunity to a value that is out of range returns the text below to the error log. You will see that now you can easily see the Guid of the target entity item and the data that is being sent in the request. This should make it much easier to diagnose issues with Dynamics CRM.
UPDATE:opportunity(731f4eed-d71d-e611-80bb-00155d016e05)
SET
actualclosedate=2016-06-08T00:00:00.0000000Z
actualvalue=1000
totalamount=79228162514264337593543950335
A validation error occurred. The value of 'totalamount' on record of type 'opportunity' is outside the valid range.
CREATE:email(70cbafc4-7563-e411-80c3-00155d010200)
SET
activitytypecode=email
activitytypecodename=(null)
attachmentcount=0
compressed=False
compressedname=(null)
correlationmethod=optionset(0)
createdby=systemuser(046d4493-e2e7-e311-80bd-00155d013a04)
createdbyname=Sean Cleaver
createdbyyominame=Sean Cleaver
createdon=2014-11-03T16:23:40.0000000Z
deliveryprioritycode=optionset(1)
deliveryprioritycodename=(null)
deliveryreceiptrequested=False
deliveryreceiptrequestedname=(null)
description=<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
</head>
<body> ... (value truncated)
directioncode=True
directioncodename=(null)
isbilled=False
isbilledname=(null)
isregularactivity=True
isregularactivityname=(null)
isworkflowcreated=False
isworkflowcreatedname=(null)
modifiedby=systemuser(046d4493-e2e7-e311-80bd-00155d013a04)
modifiedbyname=Sean Cleaver
modifiedbyyominame=Sean Cleaver
modifiedon=2014-11-03T16:23:40.0000000Z
notifications=optionset(0)
notificationsname=(null)
owneridname=Sean Cleaver
owneridtype=systemuser
owneridyominame=Sean Cleaver
owningbusinessunit=businessunit(1a8577f0-a1e1-e311-80bd-00155d013a04)
owninguser=systemuser(046d4493-e2e7-e311-80bd-00155d013a04)
prioritycode=optionset(1)
prioritycodename=(null)
readreceiptrequested=False
readreceiptrequestedname=(null)
safedescription=<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
</head>
<body> ... (value truncated)
statecodename=(null)
statuscodename=(null)
subject=Thank you for your order 205-6373703!
to=account(ccc5ef83-c210-e411-80bf-00155d013a04)
Account With Id = ccc5ef83-c210-e411-80bf-00155d013a04 Does Not Exist