The button OK on the copy.aspx (which opens when selecting “Send To-> Other Location” from Item-level menu), calls an ActiveX control called
STSUpld.CopyCtl.You can observe the file copy.aspx located at
C:\Program Files\Common Files\Microsoft Shared\Web Server Extensions\12\TEMPLATE\LAYOUTS\Copy.aspx
copyctl = new ActiveXObject("STSUpld.CopyCtl");
Now I was getting a Blank Dialog Box on Clicking Ok button on Copy.aspx. Since it’s an ActiveX, it could be a client side issue(IE-Office Integration) – and you might want to check accessing the site on another environment.
Also check following registry key, if it is there - "HKCR\STSUpld.CopyCtl"
One of possible conditions leading to this problem could be Multiple versions of Office installed (in the client environment..).
In this scenario, customer had SharePoint Designer also installed on the client machine where the issue occurs. The resolution for this case was - Open “Microsoft Office SharePoint Designer” IDE and Click on the “Help” menu to open up the list. Click on the “Office Diagnostics” help menu and wait till this operation completes.