I think, that the disk is defect. It is not possible to write a 800kb disk with modern computers, you need another Mac like a SE or SE/30 to do this. There are some tutorials in the net, but you need a Mac with a superdrive or an external 800 KB drive to do this task.
Was the floppy drive cleaned and lubricated? Sometimes cleaning the reading head with alcohol (isopropyl) solves some reading problems.
I think, that the plus can read disks from OS 1.1 up to OS 6.0.8. What is the OS on your disk?
Where are you from? Perhaps someone can send you a working disk? I can produce disks from OS 0.97 up to OS 7. But I am from germany.
But also with a working boot disk you will have the problem to get software to your computer. Even for a serial communication, which can be a solution, you must have a programmdisk for your plus.
When I came into this problem I bought a SE/30 with networkcard and an external 800kb disk drive. I can download software with my windows PC from the internet, put it in my own webserver with only standard html und download it from there with my SE/30 and Internet Explorer 3. This worked for me.