The likeliest reason is that the new client is not pointed properly. Perhaps you mapped a drive or used UNC, neither of which works with Gradience. Perhaps a character is missing. In any event, the first thing to try is to replace the ini file that the new client is using.
Where it is...
The name of this file is Hrware.ini. It is located at C:\ProgramData\Gradience. By the way, the ProgramData folder is often hidden on new computers so you may have to unhide it. If you are unsure how to do this go online for the steps to do so for your particular operating system.
How to Replace it...
If you have another client workstation that [can] connect to the data go to that computer and copy it's hrware.ini file and use that to replace the one on the new, non-working client workstation.
If you don't have another working client you can go to the machine where the database resides to copy the hrware.ini file. If you do this though, you will have to alter the [copied] file before using it to replace the bad one on the new, non-working machine. The image below shows what must be changed. Change the word Localhost to the name or the IP address of the computer/server that is hosting the data. Leave the PATH line alone! The drive letter indicated on the PATH line refers to the host machine, [not] the client.
Save what you've done and try to launch Gradience on the new client once again.
Another reason why Gradience can't open on the client workstation...
You may be running version 11 Gradience on your server, which uses an older version of Firebird than the version of Firebird used by the new version of Gradience that you just installed on the client workstation.
Firebird is the mechanism that connects the software to the data. Gradience uses the instance of Firebird residing on the computer/server where the database resides. If that computer or server is running an older version of Firebird, the software on your client will [not] be able to open.
Please be sure that you are already running this latest iteration of version 12 on your server and any other clients. If you are not, please install the latest iteration of version 12 on the server and other clients as well.
When you run different releases of [any] version on various machines that are all pointed to the same database, you will get weird, voodoo-like performance from the software and you risk corrupting the data beyond repair. Such corruption can cause functionality issues that cannot be resolved.
If the software still won't open please click here.