Mint freezes completely when logging in after switching user

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I have a dell inspiron 15r with an ATI 7670.
I don't use the graphics card at all in linux and turned it off through vgaswitcheroo.

Code: Select all

echo "OFF" > /sys/kernel/debug/vgaswitcheroo/switch

However if I switch user, after login, it completely freezes. If I don't turn of the gfx card, it works properly.
What could be the problem?