Error when accesing POWL query "You cannot currently access this service"

Hello,

We have implemented interface IF_POWL_FEEDER for the leave/attendance query in POWL. When we are trying to browse to it throught the portal we are getting the following error message, even assignning an employee to the portal user with infotype 0105/0001 we are getting the error message in the screen cap. Sometimes we get the message for some portal users and not for other using assignnig the same employee. Anyone has had this issue before?.

Thanks.