[xwiki-users] Can't delete attachment

Hi, I imported several .xar files from another xwiki instance and afterwards wanted to delete the uploaded .xar files. All but one have successfully been deleted. Everytime I delete "Xwiki_New.xar" from the import screen inside the administration screen and refresh the page it's there again. Also in document index I still see it in the attachments tab and not in the deleted attachments tab. Any hints? Is it safe to simply delete it from xwikiattachment table in the database with phpMyAdmin? My system is Windows Server 2003 R2 with Apache 2.4, MySQL 5, Tomcat 7, XWiki 6.3. Thanks in advance, Dennis