Hi,
the possible causes : Jamming or torn braking cables or corroded and stuck parking brake levers inside the rear calipers.
It is quite easy to find out: Jack up your car at the rear (or lay down under the trunk) and take a look at the levers, the parking brake cables are attached with.
If the levers (or even just one of them) aren't in their neutral position, it might look like this:
Mind the red marked lever point. In its neutral position, it must be in touch with the rest bolt. As it looks similar to this image, hang out the cable of the lever(s). If the lever snaps back into its rest position now, the cable will stuck. If the lever keeps remaining in its incorrect position, the lever itself will stuck inside the caliper.
I'm really sure, that the second option is the cause – it's a well known major bug.
Now you can try WD40 or similar and engage the lever with a pipe wrench or so, until it is moving again.
But this will normally not solve the problem for a long term.
Basically the levers look like this, after they are dismantled.
The only way to get rid of that is buying a new one or to refurbish the calipers.
