OSB error handler using fault variable can't acess fault var

There is a typical situation where you can't access the fault variable directly inside the error handler . When you got to compare and conditionally branch and when you use the fault variable in the condition then you would see error as below

 

The typical flow would look like this

This can be solved by assigning the fault variable to an intermediate value as below

Then the condition can be specified using the intermediate value as given below

Now the error goes way and every thing works fine as expected.