I get an "MMSYSTEM error 275" when I try to play a DVD encrypted movie.

This can happen if you are using the original release of Win 95 and
you have the CD-ROM drive as a slave to the DVD-ROM drive. Replace
the file ESDI_506.PDR with its equivalent in OSR2 in the
subdirectory IOSUBSYS of Windows/System. Or, you can download from
www.sigmadesigns.com - "Knowledge Base, FAQ about Hollywood Plus"
an ATAPI driver compatible with most IDE DVD-ROM drives. Other
possible reasons the installation of incompatible SCSI drivers or
an RPC2 DVD-ROM drive NOT set for any region. Some movies will
require turning ON the "Disable UDF format" as described in
point 15 below. If still problems with UDF, disable the UDF
readers of the CD burner installed.