having issues with my dropdown menu

hi all, I have two sub-menus in my drop-down menu. for some reasons every time i want to move from a menu to a sub-menu, the sub-menu disappear ?? any help please? you can check the behavior for yourself. here is the link https://dev.webgrowth.biz/ place your mouse on top of Members and try to click one of the sub-menus that appears.

just in case here is my php codes:

<ul id=”mydropdownmenu”>
<li class=”current”>Home

• Members
  <ul class=”sub”>
• Register”>Register
• Find Member”>Find Member
• Contact
• About

and my css codes:

#mydropdownmenu {
position: absolute;
top: 35px;
left: 450px;
width: 100%;
text-align: center;
font-weight: bold;
}

ul#mydropdownmenu {
list-style: none;
padding: 0;
margin: 0;
}

li {
float: left;
position: relative;
width: 100px;
text-align: left;
}

ul#mydropdownmenu li a {
display: block;
}

li ul {
display: none;
position: absolute;
width:100px;
top: 0;
left: 0;
margin-left:-1px;
}

li>ul {
top: auto;
left: auto;
}

li:hover ul, li.over ul {
display: block;
}

#mydropdownmenu a {text-decoration:none; color: white; }
#mydropdownmenu a:hover {color: black; }

body { behavior:url(csshover.htc); }