This can happen if the project being exported is too large for MSP to open.
Release : All Supported Releases
Component : CA PPM MICROSOFT PROJECT (MSP)
1. See Clarity PPM MSP Interface Performance Best Practices at: 13911 to see if there are any best practices that can be used to help reduce the size of the project (durations, # of tasks, assignments, baselines, ect)
2. As of April 3, 2018 MSP Update a configuration is available to help with this issue: