IE 7 - css background image dissapearing

once again I have come across a frustrating error in IE 7 (works fine in IE 9)

I have 5 css classes, they are all EXACTLY the SAME except for the bg image and heigt (making this the same doesnt help). However on the last one the background image is not displayed in IE7.

here the code for the element that wont work:

.sm-nav_xing a {
line-height: 23px;
font-size: 13px;
background-image:url(images/smedia/xing.png);
background-repeat: no-repeat;
vertical-align:bottom;
display: block;
}
.sm-nav_xing a:hover {
background-image:url(images/smedia/xing_mo.png);
background-repeat: no-repeat;
}

here is the link to the page:

http://www.formunddrang.de/wp/?page_id=65 (bottom right - the last line of the list "Unser Unternehmen bei" XING image is missing in IE7

Thank开发者_开发技巧s!

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your </a> tag is not closed

<span class="sm-nav_xing"><a href="" target="_blank">Unser Unternehmen bei</span>