Workspace variable not defined

Hello all, I have my model in Simulink and it runs perfectly. I wanted to add a script in m-file called using the callback OpenFcn, and in this script I want to calculate the power dissipated from all the devices in my model. I have set the workspace variable, but when I run the script, it tells me that the workspace variable is not defined. I have no idea how to solve this problem if anyone could help.

[Rik]

Could you show the part of the code that throws the error? And could you also copy the error stack (so all the red text, including the functions with line numbers)?