We've got a problem on one of our site and it's annoying our client. They can't add links to their pages via the Media Library icon in the FCKEditor anymore.

Either the Media Library pop up ignores our selection, or we get an exception.

See the screeshot below:
Screenshot

And the exception my client is getting:

Message: Index was outside the bounds of the array. 
Stack Trace: 
at CMSModules_Content_Controls_Dialogs_LinkMediaSelector_MediaView.GetArgumentsTable(String argument)
at CMSModules_Content_Controls_Dialogs_LinkMediaSelector_MediaView.GetItemUrl(String argument, Int32 height, Int32 width, Int32 maxSideSize, Boolean notAttachment)
at CMSModules_Content_Controls_Dialogs_LinkMediaSelector_MediaView.innermedia_GetListItemUrl(DataRow dr, Boolean isPreview, Boolean notAttachment)
at CMSModules_Content_Controls_Dialogs_LinkMediaSelector_InnerMediaView.ListViewControl_OnExternalDataBound(Object sender, String sourceName, Object parameter)
at CMS.UIControls.GridViewTemplate.BindData(Object sender, EventArgs e)
at System.Web.UI.Control.OnDataBinding(EventArgs e)
at System.Web.UI.Control.DataBind(Boolean raiseOnDataBinding)
at System.Web.UI.Control.DataBindChildren()
at System.Web.UI.Control.DataBind(Boolean raiseOnDataBinding)
at System.Web.UI.Control.DataBindChildren()
at System.Web.UI.Control.DataBind(Boolean raiseOnDataBinding)
at System.Web.UI.WebControls.GridView.CreateRow(Int32 rowIndex, Int32 dataSourceIndex, DataControlRowType rowType, DataControlRowState rowState, Boolean dataBind, Object dataItem, DataControlField[] fields, TableRowCollection rows, PagedDataSource pagedDataSource)
at System.Web.UI.WebControls.GridView.CreateChildControls(IEnumerable dataSource, Boolean dataBinding)
at System.Web.UI.WebControls.CompositeDataBoundControl.PerformDataBinding(IEnumerable data)
at System.Web.UI.WebControls.GridView.PerformDataBinding(IEnumerable data)
at System.Web.UI.WebControls.DataBoundControl.OnDataSourceViewSelectCallback(IEnumerable data)
at System.Web.UI.WebControls.DataBoundControl.PerformSelect()
at CMSAdminControls_UI_UniGrid_UniGrid.ReloadData()
at CMSModules_Content_Controls_Dialogs_LinkMediaSelector_InnerMediaView.ReloadListView()
at CMSModules_Content_Controls_Dialogs_LinkMediaSelector_MediaView.Reload()
at CMSModules_Content_Controls_Dialogs_LinkMediaSelector_LinkMediaSelector.HandleFolderAction(String argument, Boolean reloadTree, Boolean callSelection)
at CMSModules_Content_Controls_Dialogs_LinkMediaSelector_LinkMediaSelector.EnsureLoadedData()
at System.Web.Util.CalliHelper.EventArgFunctionCaller(IntPtr fp, Object o, Object t, EventArgs e)
at System.Web.Util.CalliEventHandlerDelegateProxy.Callback(Object sender, EventArgs e)
at System.Web.UI.Control.OnLoad(EventArgs e)
at CMS.ExtendedControls.AbstractUserControl.OnLoad(EventArgs e)
at CMS.UIControls.CMSUserControl.OnLoad(EventArgs e)
at System.Web.UI.Control.LoadRecursive()
at System.Web.UI.Control.LoadRecursive()
at System.Web.UI.Control.LoadRecursive()
at System.Web.UI.Control.LoadRecursive()
at System.Web.UI.Control.LoadRecursive()
at System.Web.UI.Page.ProcessRequestMain(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint)

What seems to be the problem?

I'm completely clueless about what could cause this error, as it was perfectly working last week...

Thanks!