Sometimes when writing DL disks, Toast seems to hang at "writing lead-out" and then crashes. I've never figured out why, tho it probably has to do with bad media. However, If you get to this stage, the disk will actually play fine, despite the crash. (At least mine do)
One secret in genereal with DL disks is to keep the VIDEO_TS folder a bit small - under 7.5GB. Most of the cheaper DL blanks seem to have coating imperfections out near the edge that cause dropouts, freezes etc. Keeping the total folder size a bit small pulls the layer change in a bit from the edge and keeps you out of this danger zone. The only disks that don't benefit from this seem to be the Verbatim DLs, which seem to be 100% reliable right out to 8.0gb.