Hey,
are you using WebIDE or Eclipse?
This error means, that somthing went wrong while bootstraping the ui5 resources.
Check your index.html.
You cand load the ui5 resources online via:
<script src="https://sapui5.hana.ondemand.com/resources/sap-ui-core.js" data-sap-ui-preload="async" data-sap-ui-libs="sap.m" data-sap-ui-theme="sap_bluecrystal" data-sap-ui-xx-bindingSyntax="complex" data-sap-ui-resourceroots='{ "<NAMESPACE>": "<FOLDER>" }' > </script>Or you can load it local via eclipse plugin:
<script src="resources/sap-ui-core.js" data-sap-ui-preload="async" data-sap-ui-libs="sap.m" data-sap-ui-theme="sap_bluecrystal" data-sap-ui-xx-bindingSyntax="complex" data-sap-ui-resourceroots='{ "<NAMESPACE>": "<FOLDER>" }' > </script>