jsapiv3.1, "dojo" undefined?

[gaolei]

when I use
<script type="text/javascript" src="http://pc01/arcgis_js_api/library/3.1/jsapicompact"></script>
it says "dojo undefined".

but if I use
<script type="text/javascript" src="http://pc01/arcgis_js_api/library/3.1/jsapicompact/js/dojo/dojo/dojo.js"></script>
it's OK

Are there any differents between them?

[__Rich_]

when I use
<script type="text/javascript" src="http://pc01/arcgis_js_api/library/3.1/jsapicompact"></script>
it says "dojo undefined".

but if I use
<script type="text/javascript" src="http://pc01/arcgis_js_api/library/3.1/jsapicompact/js/dojo/dojo/dojo.js"></script>
it's OK

Are there any differents between them?

Have you set up the default document for the jsapicompact directory? (e.g. the ESRI-supplied default.ashx is fine if you're using IIS)