Redirect loop error after login

Hi,

I have created a custom post taxonomy called portfolio so such posts have an url like this: mydomain.com/portfolio/post-name/. This is fine so far however i just found I am having a problem with my WordPress login and i believe this is causing it. I have a login link on every post so if a user log in from there it is supposed to be redirected to the post page but instead i get a redirection loop error.

If you look at the URL which WordPress is trying to redirect to you will see something like mydomain.com//post-name/ so it means the taxonomy name is missing from the URL and thats causing the redirection error.

How can i address this problem and have the redirection fixed?

Thank you.