I haven't moved any apps to the SD card, only music in fact. And the card is a class 10 so that shouldn't be the problem eiter

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I just removed the SD card from the cell phone and the web crashing, sluggish performance, apps not working is completely gone. Putting the SD card back in => problems are back.
I just dragged and dropped the files from my pc to the cell phone and I'm now reading about File expert and such, could that be a solution, transferring the files like that?
Also I can't seem to format the SD card through the cell phone, it says 'update package not available'. Could that be a problem?
Thank for the effort BTW