Your user name and the capital letter
Due to technical limitations in the MediaWiki software the first character in the page title (in essence after the namespace prefix, for example "User:") is case insensitive for most namespaces and is as a page title always rendered with a capital letter.
Looking at theit seems that while the case insensitivity can be overridden on a per namespace basis, the User namespace happens to be one of the few for which this can not be done (the two other namespaces are Special and MediaWiki). :-\
The namespaces are "classes" of pages that usually have slightly different uses and functionalities (think for example of the different ways to add categories, images and templates to a page; they are three different namespaces).
I am sorry for the inconvenience.