It has been discovered that some customers experience a problem with the PST export tool in the Wave15 version of the cloud. Specifically, the symptom is:
When a Tenant Admin attemptsto download the PST file, he or she receives "Microsoft.Exchange.eDiscovery.ExportTool.exe has stopped working" and their only option is to terminate the process.
This can be resolved in one of two ways:
1. Add outlook.com and office.com to trusted sites in Internet Explorer.
2. Install the .NET 4.5 package.
This should resolve the issue with the PST export tool.
Special thanks to mbarta for the tip!