object reference not set to an instance of object

This is such an unspecific error message and description that I think you should contact support to walk you through the process of identifying the root cause.

An Object is an instance of a Class , it is stored some where in memory. A reference is what is used to describe the pointer to the memory location where the Object resides. The message "object reference not set to an instance of an object" means that you are referring to an object the does not exist or was deleted or cleaned up. It's usually better to avoid a NullReferenceException than to handle it after it occurs. To prevent the error, objects that could be null should be tested before being used.

if (mClass != null)
{
// Go ahead and use mClass
mClass.property = ...
}
else
{
// Attempting to use mClass here will result in NullReferenceException
}

Thanks Mark.

I had a similar problem with a script that threw the error "Exception has been thrown by the target of an invocation.Object reference not set to an instance of an object." and your answer help me to resolve the problem.