Nima,
this is probably due to the ns_cache version. The 'normal' openacs version doesn't accept the same number of parameters as the newer (1.5?) version that has been around for some while. There are quite a few posts about this on the forums (I've got caught by it!)
You could put a change in the xotcl code to call with the correct params for your version of ns_cache.
Cheers
Matthew
