Firstly please make sure the latest patches are installed and XPP recompiled after patch installation.
UIM and custom script dlls are stored in the database after deployment to the server.
Please refer to KB article that contains useful information on how to deploy a custom dll onto the server and verify the results # 330508 : How do we upload custom DLL for .NET Code module onto IAServer by Captiva Designer 7.0?
Make sure to restart DCC modules/services such as Image Processor, Extraction, .Net Code and Desktop as the custom dll might be considered as “in use” by one of this module preventing to delete or update the dll with a new version.
Once the dll is deployed onto the server try to relaunch the module and verify that your custom dll is downloaded to user folder C:Users<username>AppDataLocalEmcInputAccelCustomBin.
Try to stop all DCC modules on the client host, clean up this folder and then re-launch Desktop module.
If you do not see your dlls, then something was not deployed correctly and to determine the problem it’s good to start with checking Desktop traces at C:ProgramDataEmcInputAccelCPDSKTOPTrace folder.
Hope this helps.