VWD Error Meaning?

I know that error's dont just pop out of the blue and there should be a reason for why it appears but I swear this one came out of no where, I didnt even change my sites code, it was working I did a couple refresh's got this error now I get it everytime, i restarted the program the error went away I opened up a few pages and it came right back.....

Can someone help shed some light on what this error means?

I think I may have found the reason for this error hidden inside of my code, I changed my code around a little bit and I dont seem to be having the problem anymore, I hope this has fixed it..