I am having issues connecting my HMI to my S7-1200 after a PLC firmware upgrade from V4.04 to V4.07. This used to work perfectly using non-optimized block access. However after the upgrade I can't get it to read anything and it spams the log every 10th of a second with "Error reading S7ReadResponse. Error code = 8104." 

I have below a screenshot of my protection & security settings inside the PLC. 

Most notably, Access Level is Full Access (no protection) No Password Required and then Permit Put/Get is checked. 

I have also tried using accessible devices to factory reset the password protection in the PLC. 

I am not sure what else to try, can anyone help me?

Hello evanbp

yes the new FW could be tricky. Seems to be OK from the first view...

Here is a FAQ for Unified. Also if you do not have unified you can try the different steps in the FAQ:

https://support.industry.siemens.com/cs/de/en/view/109955142

If you use WinCC V7/8 for example then you have to so the export with SCADA Export Tool and import it in the WinCC project to get the new certificate (even if you do not use it...)

Which HMI do you use?

Bye Murof