Oracle Database Discussions

hi all

i have a vb.net application with oracle 10g as Database.
my envoirnment is like this
Window Xp on server,Win Vista on Clients.
for connectiviety of clients to server i am using oracle client.
now i format my two client pc and install them again win vitsa and install oracle client and my application. but when i connect my application to server then the error occure require oracle client 8.1.7 or higher version.
i am unable to understand that why this problem coccure on my two pcs althogh rest of all clients working properly.

can any body help me.
thanks in advance