ok.. I've not been able to close the infocenter by way of the x button, however I found a way to close it. It would seem that right clicking anywhere on the window and adding the close option to the popup window that comes up will close the window.
Anyone not able to close the infocenter just edit the top line of this file "eq2ui_custom_infocenter.xml", that looks like this
"<Page Activated="true" allowcloseontop="
false" eq2usescomwndcontrols="true" Location="166,199" MinimumSize="620,250" Name="InfoCenter" OnShow="TabPages.Miscellaneous.visible=true
OnShow=' '" ScrollExtent="700,410" Size="700,410" UserMovable="true" UserResizable="true" version="1.0">
to this
<Page Activated="true" allowcloseontop="
true" eq2usescomwndcontrols="true" Location="166,199" MinimumSize="620,250" Name="InfoCenter" OnShow="TabPages.Miscellaneous.visible=true
OnShow=' '" ScrollExtent="700,410" Size="700,410" UserMovable="true" UserResizable="true" version="1.0">
Save it and close it, then log back into game.
When ye right click within the window the close option will be there and allow ye to close the window.