Sorry,I'm not familiar with portable Spybot,I've never used it yet.
I do remember having problems Immunizing the (Popups) part of Firefox immunization a long while back.If I remember it correctly,it hung on that,pretty much the way you described.So,maybe you could give this a try:
Open Spybot,click Immunize.In the window to the right,rightclick,and select "deselect all."Then,put a checkmark beside Global(Hosts),and then click the Immunize button up top,with the green cross beside it.See if Spybot will Immunize just the one item.If it hangs,just leave it for a little bit,maximum about 10 minutes.Please let me know how that goes.