30 is not a valid transparency flag. With dbSetObjectTransparency, you should use a flag between 0 and 6, the meanings of which are not documented in the Dark GDK help. Here is a quotation from Dark Basic Pro help that at least gives some guidance what they mean. Try to select the flag that works best for you.
http://forum.thegamecreators.com/?m=forum_view&t=170502&b=1&msg=2019454#m2019454
In addition to dbSetObjectTransparency, you should also use dbSetAlphaMappingOn(objectID, percentage), which tells the system that the alpha map should be used for the given object and the percentage of transparency.