Make sure your skin folder does not have any spaces in the name.
View the source of the page and copy the url for csshandler.ashx to a new browser tab, does it show css or does an error happen?
Maybe there is a mismatch between the skin and the mojoPortal version. Newer versions of mojoPortal support some theme.skin settings that were not supported in older versions so a new skin would cause errors if copied into an older version, and older skins may need to be updated according to the important skin changes.
If an error is happening start with basic troubleshooting to find the error detail.
Hope that helps,