Cannot update record

I want to capture the first value entered for "Closing Date" in a Potential. I created another date field called "Initial Projected Close Date" on the Potential form. I have a workflow triggered on the first record change on "Closing Date" that calls a custom function. I want the custom function to copy the date value from "Closing Date" to "Initial Projected Close Date".

I am using the example at https://www.zoho.com/creator/help/script/update-records-in-zoho-crm.html as a guide. Here's my code:

pid=input.PotentialId.toString();

info pid;

updateResp = zoho.crm.updateRecord("Potentials",pid,{ "Initial Projected Close Date" : input.CloseDate });

info updateResp;

Here's what I sometimes get from "info" when I run it:

Executed Successfully

Log messages:

1719128000000410107

{"message":"Record(s) updated successfully","Created Time":"2016-03-12 12:48:02","Modified By":"Chris Myers","Id":"1719128000000410107","Modified Time":"2016-03-12 14:36:00","Created By":"Chris Myers"}

But "Initial Projected Close Date" is not updated when I check the record.

I also get this result much more often. I don't understand this because I am an administrator, have checked the profile and field rights, and I own the record I am using to test as well.

Executed Successfully

Log messages:

1719128000000410097

{"message":"You do not have the permission to edit this record or the \"id\" value you have given is invalid.","code":"401.2"}

I have a CRM Plus license.

Any help would be greatly appreciated.

Chris Myers