Hi:
One time where I've seen this happen (SP runs in EG/AMO, but not the Portal) is when I used macro variables like &VAR and &CLASS which are Javascript "keywords". The Portal uses JavaScript to build the GUI for submitting the SP -- so if your SP macro variables are named the same as JavaScript keywords, it confuses the Portal and you generally get an "error on page". This Tech Support note talks about it:
http://support.sas.com/kb/18/502.html
I'm not exactly sure what the whole list of Javascript "words to avoid" are. In our Stored Process class, we recommend avoiding JavaScript functions and object names as a best practice -- for example break, do, if, throw, catch, case, enum, in, try switch, var, class...) We looked them up in a JavaScript manual.
Otherwise, if that's not it, you might check with Tech Support for more help. They can look at your SP registration and help you figure out what's wrong.
cynthia