The constructor to deserialize an object of type 'Microsoft.Exchange.WebServices.Data.ServicexmlSerialization' was not found

Is this working for some emails or not working for all emails?

Was this working before and stopped working?

If you run ConnectionStringEditor.exe in [K2 > Host Server > Bin] directory, does the EWS connection strings have the Oauth Resources parameter populated?  Or is it still using basic/password authentication?

Dear TinTex,

Thank you for your information.

This is happened only with one instance within a workflow and other instances with in the same workflow is working fine with same user.

When I checked in view flow, this is pointing to workflow email (Not a task email) which sends email to initiator that the request is initiated.

if you have any idea could be appreciated.

Best Regards,

Thriveni

If it is only specific to a single instance of a workflow, then it is perhaps bad data that is being used in the email step.  I would check and compare if any of the data fields, item references, or attachments that are being used in this email step greatly differs from a working instance.

Perhaps these data fields, item references, or attachments are empty or null or returns an error or invalid value which results in this error.

Hi @Thriveni 
Have these answers resolved your question? 

Hi,

We encountered the same issue/error and was able to resolve it by Go to Activity, as this error is more related to sending an email activity from the workflow .

Regrads

Kal