This is a broad error description and can occur for various reasons. We recommend you verify the following things:
The app is signed with a valid Ad Hoc or Enterprise certificate
If you are using an Ad Hoc certificate, the device UDID is registered for the provisioning profile that was used
The deployment target (minimum required iOS version) is not higher than the iOS version on the device
The app is configured to run on this device family (iPad OS apps may not run on iPhone)
There is enough free space on the device to install the app
Try these steps until you find the source of the error. It can also help to remove all currently installed versions of the app and reattempt the installation.
If you are still having trouble getting the app to work, feel free to contact us and we'll do our best to help you out.