Can't boot Windows after resizing OS X partition

First, here is some information about my setup. I use Mac OS X Yosemite 10.10.3 and then I have used Bootcamp to create a partition for Windows 7. This has worked perfectly since I did it a year ago, but now I have a problem.

I wanted to add more space to the Windows partition, but after just resizing my Mac OS X partition to make 20gb of unallocated space, I can no longer boot into Windows - it does not show up as a bootable disk when starting up with Option key held down.

- The Bootcamp partition does show up in Finder, and I can see my files and folders on there.

- It also shows up in Disk Utility, however all buttons for repair etc. are greyed out and it says "Write protected" when I hover over the partition. There is also a line in the bottom saying "Owners Enabled: No".

- Bootcamp also shows in Startup Disk settings, but if I try to boot to it, it says "No bootable device detected".

Here is what I did to resize the partition:

- Boot to Online Recovery Mode

- Go to Disk Utility > Macintosh HD > Partition

- Then I dialed the wheel for Macintosh HD backwards, to free up 20gb of space

- Pressed OK and it started the resize process, which completes without errors

- Restart Mac and then I can no longer boot to Windows

I have downloaded GPT fdisk but I wanted some information first, before using it. Hope someone here can guide me in this. 🙂