Cannot add existing user to a Project (Portal vs Client users???)

Cannot add existing user to a Project (Portal vs Client users???)

I have 4 admin users registered to Zoho CRM.  3 of them come up as portal users and one comes up as a client user. When i try to add the client user to existing projects the request goes through but nothing happens.  When i try to import user from CRM i get the same error.  We did not have to set anything specific for the first 3 users to view the existing and new projects.  The user which is having issues viewing the projects was also added the same way.  Please help clarify what needs to be done in order to add this user to new and existing projects.  Does the Portal vs client user has something to do with this?  I tried looking up if there is a way to convert one to the other and i could not find any info, except explaining the differences between different roles on a project.  But that still didn't answer why one of our users cannot view the project.