In your style sheet, for the selector
#sidebar ul li {
list-style-type: none;
list-style-image: none;
margin-bottom: 15px;
border-left10px solid;border-color:#ffffff;}
add a : between border-left and 10px. For the selector:
#sidebar ul ul, #sidebar ul ol {margin: 15px 0 0 20px;border-left10px solid;}
same fix. and again in
#sidebar ul ul li, #sidebar ul ol li {margin: 5px 0 0;padding: 0;border-left10px solid;}
a few lines down.
There may be a positioning issue with this theme. The page width is 950px. #content is 570px. #sidebar is 265px wide and positioned to the right of #content using margin-left of 665px (I've never liked this method, but I guess that's my issue). add a 1px border-left on #sidebar, you have 19px to play with (265+665+1). The 20px of padding-left added to #sidebar shouldn't affect anything, but you never know how browsers will add this up (especially IE).
The first thing to do is fix the errors, so that the borders are rendered as intended. I guess I would reduce the padding-left in #sidebar to 0 as a test to ensure that it doesn't have any effect, then re-instate it if it doesn't. Then reduce margin-left in #sidebar in increments to see if the sidebar moves back into place.