multisession burning not working

[Maria Paulia Belgado]

Hi,

I followed the instructions on how to burn multisession discs using the 
disk utility program (i found this in the help menu). Basically, I 
created the .dmg file of my folder, inserted a disk, burned the disc 
and clicked on "leave appendable".  Now the discs I have made (I tried 
it a couple times) will not mount on my mac. What could be the problem? 
I followed the instructions in the help menu in os x.

thanks