I was able to get this (create a link to the post author’s BP profile) to work using Boones suggestion here http://wordpress.stackexchange.com/questions/43528/how-to-get-a-buddypress-user-profile-link-and-a-certain-user-profile-field-for-t
To get it to work in the sidebar (running Genesis and the Content Aware Sidebar plugin) I had to use the code below to pull the author id outside the loop. I am strictly an amateur but this may be where folks are having trouble adding a link in sidebars, plugins or widgets?
http://wordpress.stackexchange.com/questions/39493/getting-user-id-for-the-author-meta-outside-the-loop-in-multisite
If you are like me, and not a coder, below is the exact code I used:
<?php
$temp_post = get_post($post_id);
$user_id = $temp_post->post_author;
$author_bp_profile = bp_core_get_user_domain( $user_id );
?><a href="<?php echo $author_bp_profile;?>">View the author's profile</a>
I updated to 1.5.3.1 and the issue still exists. It happens of 2 domains. I am not using .www