Well, first of all, what are you trying to accomplish with that URL?
I’m also wondering why you have set up your theme directory that way. Is the name of your custom BuddyPress member theme actually “buddypress-member”? Or, are you using the default BP member theme “bpmember”. Why is the member theme directory called /member-themes/ instead of /bp-themes/?
If I go to
http://wspinacze.pl/members
Your site works fine.
If I go to
http://wspinacze.pl/wp-content/bp-themes/bpmember/images/message_thread_back.gif
I don’t get an error. The gif image is white so it will not be visible on the default white background of your browser.
If you still have issues, then read this thread.
Hm, you’re right, buddypress-member is old name of member theme, istn’t it? I found call to that place in my error log, probably I left it somewhere in my layout modification.