If the U: (or the drive specified) shows a message "not avalible" there can be a few reasons for this.
First make sure that the userid and password is correct and the message under the user is "User verified" (or similar).
Look at this video first. https://youtu.be/CdHzI8gOBQQ?t=1m40s
If the user is ok, then try the next steps, in the following order:
1. It's normally because the driver is not installed. When the client starts a popup is shown to install the driver, please do so. Restart the client and just before the "welcome message" the pop should be shown. If there is no popup message, then the driver is installed correctly.
2. If the same user is logged in on the same PC, virtuel machine or terminal server, the drive wont start, this is due to security. It needs a personal user. Only one user with the same name can be logged in at once on the same "machine"
3. Sometimes Windows fails the encryption of the local configuration file. To fix this, use file Explorer, in the header type "%localappdata%" this will take you to your local folder. Here you need to enable hidden files. to see a folder called "RfUserData", in here the configuration file "ClientPcConfiguration.cfg" is located. To check if it's the encryption fail, try to open it in notepad. If you cant do this, because of missing authority. Please delete it. And try to restart the client Again, it should ask for user id and password Again.