A workaround is to add the following CSS rules to the DialogsCssFile stylesheet:

.reLightweightDialog.RadForm_BlackMetroTouch.redLinkManager body,
.reLightweightDialog.RadForm_Bootstrap.redLinkManager body
{
	width: 540px;
	height: 540px !important;
}

/*or use that, which will affect all skins: */
/*.reLightweightDialog.redLinkManager body
{
	width: 540px;
	height: 540px !important;
}*/