ERROR #"502" when accessing groups

[Franco, Ruben]

Running Redhat 7.2 with INN 2.3.2 Rel. 5. 

     Whenever a user tries to access a group via a newsreader (such as,
outlook express), they get the following error:

"502 You have no permission to talk.  Goodbye."

     In the "news.notice" log I can see the following message:

news nnrpd[25211]: ? cant gethostbyaddr <USER's IP ADDRESS HERE> Unknown
host -- using IP address for access
news nnrpd[25211]: <USER's IP ADDRESS HERE> connect
news nnrpd[25211]: <USER's IP ADDRESS HERE> no_permission

     Is the problem with my INN configuration or is it Redhat?