My pokemon platinum game freezes on my r4

Well i have an r4 and i have pokemon platinum and some other games but their not the case well on pokemon platinum i made it to the part were cyrus opens the portal to negative world...and when cinthia comes and tells me to go in right when im about to go in the blue circle of the middle of the portal turns into a square and the game freezes. and also something that used not to hapen is that in the introduction video in the part were the portal appears the game freezes also this used not to hapen before i made it to the part where cyrus opens the portal...ps.none of my other games on my r4 freeze and i would peffer a solution that does not include formating the memory card(2gb)