1. Edit C:\Program Files\Microsoft DPM\SQL\MSRS10.MSDPMV3BETA1EVAL\Reporting
2. Set the SecureConnectionLevel to 0 if the current value is 2 (A value to 2 means secure connection is required)
3. Go to Services snap-in and restart all SQL Services.
4. Start the DPM 2010 beta installation again. That should do the trick and your DPM 2010 installation will successful.