Affected:  matrix text/dropdown file upload column.

(Regular respondent file upload works fine)

SerializationException: Type 'System.Web.HttpPostedFile'

Happens when your web.config is set to store session to SQL server database.


change from this

  <sessionState mode="SQLServer" stateConnectionString="tcpip=127.0.0.1:42424" sqlConnectionString="data source=yourserver\MSSQL2017EXPRESS;user id=youruser;password=yourpassword" cookieless="false" timeout="20"/>


to this


<sessionState mode="InProc" stateConnectionString="tcpip=127.0.0.1:42424" sqlConnectionString="data source=127.0.0.1;Trusted_Connection=yes" cookieless="false" timeout="60"/>


and the error will go away.