Error (Arduino support software): "undefined function or variable 'a'" directly after variable 'a' is stated

I am getting a error with undefined variable 'a', directly after 'a' is stated. Why is this? It is very clearly defined and in the workspace. I have attached a screenshot of the command window. The arduino uno correctly connected in the arduinosetup and 'a = arduino' was the first line of the m file 'untitled99.m'.

Is this error because I was calling 'a' in an original function? If so, how can I fix this problem? Thanks in advance.

Using Matlab2017a on MacBook Pro 10.12.1

[Jan]

Please post the relevant lines of the code. What happens before the line 53?