ADB error - read only file system

When trying to deploy an apk file to my android device using adb, I get the following output to the command prompt:

 Success
 rm failed for -f, Read only file system

The app ends up installed on the phone, but it won't run (I would imagine because of this error!)

Using 'build and run' from unity I can install other projects to the device perfectly fine. There is a long winded reason I'm not simply using Build and Run in this instance, which I probably don't need to go into.

Is there something I can do to solve the 'error' that appears?

Thanks.