Collection was modified; enumeration operation may not execute.

This error was happened in my Asp.net c# project ,specifically in a for loop iterating through the contents in a list . 

My code something like this :

 foreach (RequestContent content in  Contents)

{

    do something 

}

I googled for this type of error and finally got a solution .

I changed the code to :

 foreach (RequestContent content in  Contents.ToList())
{
    do something 
}
 and it worked fine.

The issue was that Contents was getting modified inside the loop. Calling Contents.ToList() copies the values of Contents to a seperate list at the start of the loop .No one can access this list . so nothing can modify it inside the loop and it worked perfectly .