Error when making plain text of a html body

Hi guys,

We have some email templates reusing each time. This time i copied and changed the tokens and some styling in the html body of the content.

Now when trying to make the html into plain text I got an error;

An error of type org.postgresql.util.PSQLException occurred for customer with e-mail:123@123.nl

ERROR: invalid byte sequence for encoding "UTF8": 0x00

Stacktrace:

com.mendix.core.CoreRuntimeException: com.mendix.systemwideinterfaces.MendixRuntimeException: com.mendix.core.CoreException: com.mendix.core.CoreRuntimeException: com.mendix.systemwideinterfaces.MendixRuntimeException: com.mendix.systemwideinterfaces.connectionbus.ConnectionBusException: Exception occurred while inserting data. (SQL State: 22021, Error Code: 0)
	at Admin.User_CreateEmail (Change : 'Set email data based on user and template')
	at Purchase.Confirmation_SendEmail (SubMicroflow : 'User_CreateEmail')

I did not change anything then copying pasting the old html file in note pad. Is it possible that I paste some other stuff which he tries to make plain but simpilly can not?

Anyone an idea how I can check the plain texts validaty?