You've enabled dx11 in your wow clients but aren't using the dev build that supports it.

Either use the dev build or rever to dx9. The long way to do the latter is edit each config.wtf and delete the line that starts "SET gxApi"

The short way is to delete ALL the config.wtf files, start wow once using the '-d3d9' switch and then go back to multiboxing. ISBoxer will rebuild the config.wtf files it needs.