Assignment

I'm getting this Javascript error, referencing different lines of code in the /mod/assignment/details.php file, when I try and add assignments: line 151 for Online Text assignments, line 114 for Offline Activity assignments, and line 155 for Upload a Single File assignments. In all cases, the actual line of code causing the errors is 'var config = new HTMLArea.Config();', however, it appears that the contents of the details.php file vary depending on the type of assignment (hence the different line numbers for this line of code based on assignment type). The errors occur after setting up the details of the initial edit assignment page and hitting the Next button. I'm using IE6 and am running the site (1.5.2) under IIS5.

Thanks in advance!