If you are having trouble getting your Dreamcast to boot Volgarr then download my cdi of it below.

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Here is the Volgarr the Viking cdi with the dummy file added so that it works for those of you that are having trouble booting it.
http://www94.zippyshare.com/v/4A3xuSX5/file.html
Download the file, unzip it, and then burn using the software program of your choice. I used Disc Juggler to burn mine but you can use imgBurn, Bootdreams, Alcohol 120, or any other Dreamcast cdi burning software.
Burn and enjoy!
Any problems let me know. I played the first level and everything worked. I own the game on Steam and I didn't notice any difference.
Zipped file is ~37 MB, unzipped volgarrbig.cdi is ~771.9 MB.
Burn it on a regular 700 MB CD and it will work. Almost all Dreamcast cdi games are over 700 MB. The extra #MB of data isn't burned to the CD but it's a map/blueprint for the program burning it, it's telling it how to place the data on the CD.
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Specifics of what I did:
I used Isobuster to extract the three files in the original cdi. I then used Bootdreams to add the dummy file and rebuild the cdi.