HTTP 500 error on SAP UI5 library load

Hi experts,

I have a simple UI5 application hosted on a SAP Portal 7.3.  Sometimes the page is not able to load the sap-ui-core.js library.

Following the documentation  I place the following code on top my HTML page:

    <script

         id="sap-ui-bootstrap"

         src="/sapui5/resources/sap-ui-core.js"

         data-sap-ui-theme="sap_goldreflection"

         data-sap-ui-libs="sap.ui.commons,sap.ui.table,sap.ui.ux3">

   </script>

If I launch the page I get an HTTP 500 error on the load of the core library. The exeption on the server looks like

The strange thing is thta sometimes it works and sometimes it doesn't. Sometimes the core library is loaded and I get the error on other dependencies.

I use just an HTML page and don't have UI5 applications deployed on the server.

Any suggestions?