Calculations.ConvertValue gives an error every time

[KarlaK-fl]

This is for Dynamics 365 Sales Enterprise (online).
I have a text field to contain a tax year (so that it isn't displayed with a comma).
Each year, I need to add 1 to the year, and then convert that result to text.
I tried using ConvertValue to convert my text field to a number but it gives an error every time.
I even tried just typing in the number 2018 as the input and it also gave an error.

Here are the outputs from the activity:
Original Tax Year: 2018 [This is the value of my single line of text field]
Convert processing error: True [I don't have any way of knowing why this is an error]
Convert string to Float: 0
Convert string to Decimal: 0
Convert string to Rounded: 0
Convert string to Truncated: 0

[KarlaK-fl]

I also tested it in our Dynamics CRM 2016 version 8.2 on-premises and had the same issue.