This error is caused by unrecognized environment variable XILINX. Since this variable is not defined, Modelsim can't find the specified path for glbl.v.
You can verify whetherthe variable is set by running the following command in ModelsimTranscript.
The simulation script assumes that you have built XILINX environment prior to running simualtion.
To resolve the error, perform either of the following operation.
1) A Windows user can launch the "ISE Design Suite Command Prompt" utility, located in the Accessories folder within the Xilinx ISE Design Suite 12.x Start Menu program folder, and start Modelsim in that prompt.
A Linux user can run "source <ISE 12.x installation path>/settings32.csh" (or settings32.sh depending on your shell), and then launch Modelsim GUI.
2) Modify the simulate_mit.do and replace $env(XILINX) with the full pathname on your machine.