Sorry, it seems that there are no available payment methods for your state.

Can you screenshot me the settings you’re using for COD?

Yes. Here are two images, the COD setup and the checkout setup. Thank you!
https://www.dropbox.com/s/xcjy00eifkj9ha1/checkout.jpg?dl=0
https://www.dropbox.com/s/8x7pt8uwmmpzd3y/cart.jpg?dl=0

What is the reason for the exclusion rule on shipping?

You’re referring to the ‘enable for shipping methods’ setting? They only have one shipping option. I was trying different things to make that error go away, obviously setting that rule didn’t help since I still have the error.

I really don’t understand the sporadic nature of the error. Sometimes it works, and then two minutes later it doesn’t. Makes it very hard to diagnose.

Thanks!

I’d remove that option because that adds extra dependencies on shipping. Post your status report so we can see everything being ran.

Thanks and here you go:

### WordPress Environment ###

Home URL: https://scart.blessey.com
Site URL: https://scart.blessey.com
WC Version: 2.5.5
Log Directory Writable: ?
WP Version: 4.1.1
WP Multisite: –
WP Memory Limit: 256 MB
WP Debug Mode: –
Language: en_US

### Server Environment ###

Server Info: Apache/2.4.16 (Unix) OpenSSL/1.0.1e-fips mod_bwlimited/1.4
PHP Version: 5.4.44
PHP Post Max Size: 50 MB
PHP Time Limit: 30
PHP Max Input Vars: 1000
SUHOSIN Installed: –
MySQL Version: 5.5.48
Max Upload Size: 50 MB
Default Timezone is UTC: ?
fsockopen/cURL: ?
SoapClient: ? Your server does not have the SoapClient class enabled - some gateway plugins which use SOAP may not work as expected.
DOMDocument: ?
GZip: ?
Multibyte String: ? Your server does not support the mbstring functions - this is required for better character encoding. Some fallbacks will be used instead for it.
Remote Post: ?
Remote Get: ?

### Database ###

WC Database Version: 2.5.5
:
woocommerce_sessions: ?
woocommerce_api_keys: ?
woocommerce_attribute_taxonomies: ?
woocommerce_termmeta: ?
woocommerce_downloadable_product_permissions: ?
woocommerce_order_items: ?
woocommerce_order_itemmeta: ?
woocommerce_tax_rates: ?
woocommerce_tax_rate_locations: ?

### Active Plugins (10) ###

Heartbeat Control: by Jeff Matson – 1.0.3
P3 (Plugin Performance Profiler): by GoDaddy.com – 1.5.3.9
Simple No Comment: by Jitendra Singh Dikhit – 1.0
Storefront Site Logo: by Wooassist – 1.2.0
WooCommerce Advanced Notifications: by WooThemes – 1.1.19
Woocommerce Poor Guys Swiss Knife: by Uli Hake – 2.2.4
WooCommerce Table Rate Shipping: by Bolder Elements – 3.6.6
WooCommerce: by WooThemes – 2.5.5
WooThemes Helper: by WooThemes – 1.6.1
Wordfence Security: by Wordfence – 6.0.25

### Settings ###

Force SSL: –
Currency: USD ($)
Currency Position: left
Thousand Separator: ,
Decimal Separator: .
Number of Decimals: 2

### API ###

API Enabled: ?
API Version: 3.1.0

### WC Pages ###

Shop Base: #4 - /shop/
Cart: #5 - /cart/
Checkout: #6 - /checkout/
My Account: #7 - /my-account/

### Taxonomies ###

Product Types: external (external)
grouped (grouped)
simple (simple)
variable (variable)

### Theme ###

Name: Storefront
Version: 1.6.1
Author URL: https://www.woothemes.com
Child Theme: ? – If you're modifying WooCommerce on a parent theme you didn't build personally
then we recommend using a child theme. See: How to create a child theme

WooCommerce Support: ?

### Templates ###

Overrides: –

I’ve seen “Woocommerce Poor Guys Swiss Knife” cause issues like this in the past.

Turning off the Swiss Knife seems to have solved this. I’ll keep testing, just in case it’s not. Thanks for your help.