Hello and thank you very much for your answer! That/this was/is the response in SOAP log (I just deleted Style/css info): 

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Input to Web client with SOAP action = urn: submitFile ERROR # 6243: HTTP request to SOAP WebService returned response with unexpected CONTENT-TYPE: text / html; charset = utf-8.
Input to Web client with SOAP action = urn: submitFile ERROR # 6243: HTTP request to SOAP WebService returned response with unexpected CONTENT-TYPE: text / html; charset = utf-8.
HTTP Status 500 - Internal Server Error.
The server encountered an unexpected condition that prevented it from fulfilling the request. javax.servlet.ServletException: An error occurred
see.fohm.sminet.util.CheckFilter.doFilter (CheckFilter.java:38)
org.apache.catalina.filters.ExpiresFilter.doFilter (ExpiresFilter.java:1232). Apache Tomcat / 8.5.39 (Ubuntu) End.
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We run in windows, not Ubuntu so it must come from their service 
Regards Michael