Have to made any modifications to forum.asp?
It looks like you started to install the Message Icons MOD (or removed it) and didn't take out the extra column that is used by it.
Look for this code in forum.asp:
<tr>
<td align="center" bgcolor="<% =strHeadCellColor %>"><b><font face="<% =strDefaultFontFace %>" size="<% =strDefaultFontSize %>"> </font></b></td>
<td align="center" bgcolor="<% =strHeadCellColor %>"><b><font face="<% =strDefaultFontFace %>" size="<% =strDefaultFontSize %>"> </font></b></td>
<td align="center" bgcolor="<% =strHeadCellColor %>"><b><font face="<% =strDefaultFontFace %>" size="<% =strDefaultFontSize %>" color="<% =strHeadFontColor %>">Topic</font></b></td>
<td align="center" bgcolor="<% =strHeadCellColor %>"><b><font face="<% =strDefaultFontFace %>" size="<% =strDefaultFontSize %>" color="<% =strHeadFontColor %>">Author</font></b></td>
<td align="center" bgcolor="<% =strHeadCellColor %>"><b><font face="<% =strDefaultFontFace %>" size="<% =strDefaultFontSize %>" color="<% =strHeadFontColor %>">Replies</font></b></td>
<td align="center" bgcolor="<% =strHeadCellColor %>"><b><font face="<% =strDefaultFontFace %>" size="<% =strDefaultFontSize %>" color="<% =strHeadFontColor %>">Read</font></b></td>
<td align="center" bgcolor="<% =strHeadCellColor %>"><b><font face="<% =strDefaultFontFace %>" size="<% =strDefaultFontSize %>" color="<% =strHeadFontColor %>">Last Post</font></b></td>
remove one of these lines:
<td align="center" bgcolor="<% =strHeadCellColor %>"><b><font face="<% =strDefaultFontFace %>" size="<% =strDefaultFontSize %>"> </font></b></td>
<td align="center" bgcolor="<% =strHeadCellColor %>"><b><font face="<% =strDefaultFontFace %>" size="<% =strDefaultFontSize %>"> </font></b></td>
you only need 1 of them.