[xwiki-devs] Does DB2 support virtual wiki?

Hi, I am new to XWiki. I was trying to set up virtual wiki using DB2 v9.1 or v9.5. First I installed XWiki Enterprise Manager on Tomcat and set up DB2 following the "Installation DB2" guide. After that I tried to create virtual wikis using XEM. But when I clicked "Create new wiki" link in the XWiki Enterprise Manager and enter "wikitest" as wiki identifier, it kept prompting that "A database with this identifier already exists". But the fact is that I don't have a database named "wikitest" on my DB2. Then I found out that no matter what I typed in the wiki identifier text box, it all prompted "A database with this identifier already exists". This prevents me from creating a virtual wiki. Can anyone help me out? Thanks very much in advance! BTW, I can successfully create virtual wikis on MySQL and access them.