https://bugs.freedesktop.org/show_bug.cgi?id=100242
--- Comment #4 from Christian König deathsimple@vodafone.de --- The maximum size for allocations in VRAM on radeon are usually 256MB minus pinned system resources like GART.
The game tries to allocate something which is 256MB in size, so that won't fit.
Either the driver tries to allocate a temporary buffer which is way to large or the game tries to allocate a texture which is way to large.