SUNSKYSOFT  Thank you for the report.

This problem might be solved by starting after the preferences file is deleted.

Preferences file is in the following:

/ Library / Preferences / jp.sunskysoft.DMGConverter5.plist

This problem seems to occur uncommonly.  
(Version 5.2)

SUNSKYSOFT  Thank you for the report.

Can the dmg file made by using other software (FreeDMG,DropDMG,etc) on OS X 10.6 do the mount with OS X 10.5 or less?

Time might hang in the fix of this problem because the author is not using OS X 10.6 (GM) now. (and doesn't have OS X 10.6 (GM).)  
(Version 5.2)

SUNSKYSOFT  Thank you for comment.

DMGConverter translated Japanese to English by translation software, because the English user had requested translation. However, the translation software seems not to be translated correctly. . .

Moreover, because I cannot read/write English so much, it might be difficult to correct the mistake of English.   
(Version 3.5.5)