Hi I believe Sue_H has the correct answer. After reading these posts:
 https://stackoverflow.com/questions/33727844/c-sharp-clr-throws-security-exception-unless-marked-as-unsafe

and
https://docs.microsoft.com/en-us/sql/relational-databases/clr-integration/security/clr-integration-code-access-security

I changed the Permission level under the SQLCLR project setting to...