Getting Error Code 2 error text: ""Invalid Input"" and no error detail for API_addRecord

Hello,
I am attempting to use the QuickBase API to add a record to one of my databases.

I added a record through the API once, and only once, perfectly fine, but now, with the same code and parameters, I am getting an error with no details as to what is wrong.

All of my required fields are filled in - I know this because I took them away and I get an error code 50, Missing Required Field if I take one out.

My request looks as follows:

POST /db/db_id HTTP/1.1
Host: demo.quickbase.com:443
Content-Type: application/xml
QUICKBASE-ACTION: API_addRecord
Cache-Control: no-cache

<qdbapi>
<ticket>auth_ticket</ticket>
<apptoken>app_token</apptoken>
<field fid='10'>First</field>
<field fid='11'>Last</field>
<field fid='13'>Test Data</field>
<field fid='15'>Test Data</field>
<field fid='17'>Test Data</field>
<field fid='18'>AK</field>
<field fid='19'>55555</field>
<field fid='20'>(555) 555-5555</field>
<field fid='22'>(555) 555-5555</field>
<field fid='23'>test@data.com</field>
</qdbapi>

and my response looks as follows:

<?xml version="1.0" ?>
<qdbapi>
    <action>API_addRecord</action>
    <errcode>2</errcode>
    <errtext>Invalid input</errtext>
</qdbapi>

Any help would be appreciated very much.
Thank you!