Data Conversion Error, SQL

Msg 8114, Level 16, State 5, Line 1 Error converting data type varchar to numeric.

Below is the code that I am using and the schema for the fields mentioned in the code. Some context behind this, I have a set list of indcodes. I only give one below but there are 350 in total. It is quite likely when i query by indcode, area, and ownership that the data does not exist. Hence, why I have the isnull language. Finally, I need rows that contains a value of suppress = 1 to show up as N/A.

For every indcode that I query, I need a result. The result could be actual data or some text (NULL, N/A, etc).

Last is the intended result. I only gave code for one indcode but have included six to give the example some depth.

select
CASE
WHEN suppress = 0 then isnull (mnth1emp, 0)
ELSE 'N/A'
END as mnth1emp,
CASE
WHEN suppress = 0 THEN isnull...