I am not able to access "Document Manager" portlet in Websphere Portal 6.0

I have created one user whose username and password length is 35 character l
ong.
then i added thar user into "wpsadmins" group, So it became admin user.
Then i did successful log in into websphere portal. But when i tryed to open
 "Document Manager" portlet then i got following error:

"The credentials supplied to this portlet are not valid. Contact your admini
strator for more information."

Even though i have admin credentials, i am not able to access "Document Mana
ger" portlet. On the other hand, if i create user whose username and passwor
d length is
5 and add that user into "wpsadmins" group, i can access "Document Manager" 
portlet successfully.

What could be the problem ? is it because of length of username and password
 ?

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