First up, try logging out, restarting your browser then logging back in. That should reset any error messages.
You can either host your photos on a photo hosting site like the myswag gallery or Photobucket or similar. Then you just post the link to your photo into your post. There's a button up above the text box under the "Bold Text" button to insert an image.
Or the easiest way is to just attach them to your post. But your photos need to be small (in kb terms). So either take them on a low resolution setting or resize them. I like this free program
http://www.irfanview.com/ for resizing. Go to "Image" and "Resize/Resample" then choose "640x480 pixels" which seems to work well for myswag. OK, last step, under the text box there is "Additional Options". Click on that and under "Attach" browse to where your photo is located on your computer and attach it. When you hit "Post", the photos you have attached will be at the bottom of your post. Max off 5 photos. If you have more, hit "Reply" and attach them.
Let me know if you need help further.
KB