Syncing one or more projects from Rally to Clarity fails with the following error in bg-ca.logs: 

ERROR 2020-07-19 19:35:01,283 [Dispatch Synchronize Agile Central : (tenant=clarity)] rest.validation (clarity:.....:Synchronize Agile Central) ExceptionInfo ::  Could not create resource. Resource name: tasks. Error code: projmgr.DUPLICATE_EXTERNALID_TASK Error message: PRJ-07006: Invalid or duplicate task ID. Task ID must be unique within a project.
ERROR 2020-07-19 19:35:01,287 [Dispatch Synchronize Agile Central : bg..(tenant=clarity)] ppm.rest (admin:.....:Synchronize Agile Central) CustomerResourceHandler ::  exception occurred while performing action:create
com.ca.ppm.rest.exception.BadRequestException: PRJ-07006: Invalid or duplicate task ID. Task ID must be unique within a project.

ERROR 2020-07-19 19:35:01,312 [Dispatch Synchronize Agile Central : .... (tenant=clarity)] ppm.agl (clarity:admin:.....:Synchronize Agile Central) 
java.io.IOException: 400
projmgr.DUPLICATE_EXTERNALID_TASK
PRJ-07006: Invalid or duplicate task ID. Task ID must be unique within a project.
 at com.ca.ppm.rest.client.RestApiJavaClient.validateResponse(RestApiJavaClient.java:297)
 at com.ca.ppm.rest.client.RestApiJavaClient.doPost(RestApiJavaClient.java:182)
 at com.ca.ppm.agl.connector.ClarityConnector.createTasks(ClarityConnector.java:1090)
 at com.ca.ppm.agl.services.TaskSyncManager.syncClarityTasks(TaskSyncManager.java:263)
.........
Caused by: java.lang.Throwable: projmgr.DUPLICATE_EXTERNALID_TASK

Release : 15.7.1

Component : CA PPM SAAS RALLY

1. Manually delete the integration created tasks on the project that have no assignments, then rerun the sync job.
   1. Note: It's recommended to take an export to excel of the tasks prior to performing this action as a backup. 
2. If this isn't a viable option or further assistance is needed, please contact Broadcom support for assistance.

See KB: 141061 for tips on how to optimize use of Self Service for Clarity