Howto display error message in BSP-Application UWS_FORM_PUBLIC in SRM

I created an error message within CL_IM_BBP_FORM_RUNTIME Method IF_EX_UWS_FORM_RUNTIME~FORM_ON_EVENT as return value of et_message that does not get displayed.

Instead, i can see an empty input at the top of the page.

Anything i am doing wrong ?

The XML shows that message exists:

<uxx:messages>

  <uxx:message type="E" id="ZSRM_KS" number="666" field="//survey/G21/TE18" message_parameter="" persistent="" message_v1="TEST" message_v2="TEST" message_v3="TEST" message_v4="TEST" key="0 ">TEST TEST TEST</uxx:message>

</uxx:messages>