Issue
During a Riva Cloud or Riva On-Premise sync cycle between Exchange and NetSuite, the same error is reported for multiple accounts in the Riva Service Monitor.
Cause
For NetSuite web services, it appears as though a special license type needs to be installed (applied) to allow for concurrent access to NetSuite.
Solution
The license type called a "Web Service Plus license" allows for concurrent web service access for a particular account. If you have this license enabled, you can apply the "Concurrent Web Services User preference" as described on a NetSuite.com page that requires user authentication: https://system.netsuite.com/help/helpcenter/en_US/Output/Help/SuiteFlex/WebServices/STP_WebServicesPlus.html#1059386. Another NetSuite.com page may shed light on the issue, but you need to register to see it: https://usergroup.netsuite.com/users/forum/platform-areas/web-services-suitetalk/419292-question-about-concurrency#post419292. A cached copy of the latter page can be accessed without registration or credentials at https://netsuitehub.com/forums/topic/question-about-concurrency/.
After applying the license type, enable concurrent web service access on the NetSuite user or users that are configured as target users in the Riva sync policy.