Step 1: Start Crossover and open the Run Command.
Step 2: Choose the Guild Wars 2 Bottle. Type in 'regedit'. Click on 'Run'.
Step 3 & 4: Got to 'HKEY_CURRENT_USER/Software/Wine/' and create a new Key with the name 'Direct3D'.
Step 5: Create a new 'String value' and give them the name 'FixedVShaderLimit'.
Step 6 & 7: Modify the value of the new string. It can be between 250 and 500, 275 works fine for me.
Step 8: Create the other strings. Those needed on most systems for running Guild Wars 2.
SafeVsConsts = enabled
UseGLSL = enabled
VideoMemorySize = 256 (this value depends on your video memory)
I hope this helps!