All of Andre's suggestions are good ones, especially the last of of trying to IMport the client. This is probably what failed.
The client context is just a refelction of what is in the cell_info file (you did not specify if teh Cell server is UNIX or Windows, so, I can't be more specific)
I would first check the client system to be sure of what version of DP is on there, from the MS-DOS prompt
cd \Program Files\Omniback\bin
vbda -ver
If the correct version is shown, then check the cell_info file, find this hostname of the client, and, in that line, you will see what version the Cell Server thinks it has. If it is incorrect, you can just edit the file, because that is all an Import does
Your version of DP is well out of support, so the REsponse center would not be able to help with this problem