There are a couple possible solutions for this issue.
One is to set up the Altiris PXE Config Helper service to restart when it crashes.Another option was documented on Symantec's Connect community website here. In this article, it is explained how to configure to Altiris PXE Config Helper to ignore the status of the Altiris PXE MTFTP Server service. By doing this, the status of the Altiris PXE MTFTP Server may not display in the status tab of the PXE Configuration Utility, but the Altiris PXE Config Utility shouldn't stop when making changes to the PXE configuration.
Deployment Server 6.8 SP2 (possibly earlier) through Deployment Server 6.9 SP4