When I just paste a link into the body of my text, I normally get an error message saying something has gone wrong. Here's the best way to do, quickly, easily and without fault.
Go to the website and copy the link to the clipboard.
Type a few words into the text box regarding the link, such as, 'Click here for more information', or something along those lines. The, highlight that text.
Return to your forum post, and click on the chain link picture in the toolbox at the top of the text window. It is just between the strike through icon and the double quotes icon.
This will open a box with two text fields.
Past the link into the top text field.
The text you have highlighted should appear on the bottom text field, this will be link people need to click on. You could, in theory, past the link into both boxes, but this doesn't look as professional or cool.
Click the Insert button, job done.
Give this a go, and see if it solves the problem.
MG