When I try to connect to databse from HP box using the following command

sqlplus <username>@<databasename>

I get this error message:

ksh: <database name> : not found

I can connect to the database outside the UNIX box using sqlplus though.

Looks like the problem is the way HP Unix is interpreting the the key "@"

Can someone help with this?

What happens when you type sqlplus by itself? You should be prompted with something like this:

Yes, that works

Type:
stty -a
You will probably see
intr = DEL; quit = ^\; erase = ^H; kill= @

Use the command:
stty intr ^c kill ^?
to fix that.

or else just put \ (backslash) before @ in ur sqlplus command.