Calculate Field Error

[Madam]

I am having an issue with my python script in using the calculate fields, when converting and trying to use BuildCablesMax it doesn't run as it says i have not defined the variable despite calling it earlier in my script as seen, have tried quotation marks and have run the prior cell that calls it with it declared, wondering how i can resolve the issue 

[DanPatterson]

can you show the expression  code used? It looks like 2 things got concatenated