If statement not working with error message

Hi,

try to catch simple error message in transaction COHV:

in a script with if statement:

but the system ignor, if i change the script to copy value instead of if statement:

i get the following error:

this was done based on this example:

https://www.youtube.com/watch?v=oGROQPklgYY

but it is not working, does any one has any suggestion how to solve this problem?