In two cases you need to change the current user account. First when you start mindv without login first. This can happen when you start mindv by inputting this url : http://mindv2.cloudapp.net/ , or on the home page of http://www.mindv.com/, clicking on the mindv logo. They both start mindv as a guest user .
So after mindv starts, you need change your user account by clicking on the "Change user" image button on the tool bar.
When you try to change user account, you need known that, all the document will be closed automaticly. So if you already have created a mind map, you may need save it in guest's folder first or discard it .
There is another condition, if you have created a mind map, then you left . After several hours later, you come back to continue you work, and finally try to save it . At this time a login dialog box appears asking you to sign in again. If you have more than one user accounts, you must be sure not to change the user account, or your works will be discarded.
Download MindV help files from download.com:
http://www.mindv2.com/ (Simplified chinese)
http://tw.mindv.com/ (Traditional chinese)
http://mindv2.cloudapp.net/ (Start mindv as guest user )
http://hi.baidu.com/mindvsales/blog (Hanson's simplified chinese blogs)
http://cn.linkedin.com/pub/hanson-chen/28/464/89a (Hanson's linkedin home page)