user name can be numeric ?

my Bitweaver allows user registration with username(not real name) as 'numeric' value and also alphanumeric. The problem I see is when I click on user profile with numeric value it gives error message, if username is alphanumeric it will work fine.

Example. if username is '1234'
when I click on user profile i.e. bitweaver.org/users/1234
it gives me error 'The following user couldn't be found: 1234'

if user name is 'mmln' or 'mmln1234' it will not have any problem if I click
bitweaver.org/users/mmln or
bitweaver.org/users/mmln1234

is it a bug ? or some settings were wrong.

Sounds like a bug to me. I don't know of any setting in User Package that would be fine tuning this. You could submit this to Bitweaver's bug tracker on sf.net: http://sourceforge.net/tracker/?atid=749176&group_id=141358 ("add new").