I got the same problem here! After grabbing the Grand Star at the end of the first boss, the screen just remains black. But i still can open the Wii menu or connect/disconnect a Wiimote...
Tried with different revisions (6526, 6535, 6575, 6587) but without luck. Someone experienced the same problem? Any clues to resolve this? Thanks.
It's a DSP_HLE issue.
You need to disable audio in the HLE plugin or use the LLE plugin (requires the dsp rom and coef to be dumped from a Wii or Gamecube) else you will get a black screen after getting a grand star. There's nothing else that can be done for now. Note that you will need to play the entire level without audio unless you use the LLE plugin, which is slower than HLE.
Wow, never thought it could be a sound related issue... I tried to disable audio in the HLE plugin but still this damn black screen after the Grand Star (tested with revisions 6592, 6595 and 6601)! I read in the forum that there is no dumping tool for the DSP Rom or COEF, so I suppose I'm stuck at this level... Any other idea maybe?
Anyway, thanks for the reply and keep the good work going, Dolphin Team!

Did you shut down the game -> disable all options in HLE audio, put the volume @ 1% -> start the game -> play the entire level (DO NOT USE SAVESTATE) ? That fix works for me @ every grand star.
Thanks slaQ! You were right, I disabled all options, put the volume @ 1%, didn't load a saved state and it worked!
OK, now I just hope that a fix will be out before the next Grand Star

Still no resolution for this issue? Because new Dolphin revisions do not allow to fully disable DSP audio and game always freezes after grabbing a Grand Star...

yea my dream is to be able to play the mario galaxy games on dolphin in 1920x1080, it's clearly the best games for the system (the only games that really interests me for wii).. i keep coming back here every 6 month or so to see if its been solved, only to be disapointed, but it's a nice emu and i hope it some day will be resolved
Find the LLE plugin somewhere in this forum
and in sound options enhable it.
if this still doesnt work, read the first page and the other thread ;o