1. What operating system on your PC?
2. What exactly is given the error - the PC or phone?
3. What mode is your USB storage set to - Media Device (MTP) or Camera (PTP)?
4. Is USB debugging turned on?
5. What are you trying to do?
1st step is done and nexus 4 shows on PC with MTP option selected on phone. However when trying to double click to access folders of nexus4 error comes as you do not have permission to access this device.
You can try to install Nexus 4 drivers on your PC. Here's a link usb_driver.rar (found it off xda-developers website). Or you can google search "Nexus 4 usb drivers". I'm not sure if this would solve your problem but definitely worth a shot if nothing else is doing it for you.