UPDATE: An anonymous poster left a great comment about internal names. Be sure to read it.
When working with event receivers and other code that references SharePoint list items via the object model, I often make mistakes that generate this error at runtime:
Error loading and running event receiver Conchango.xyzzyEventReceiver in xyzzy, Version=1.0.0.0, Culture=neutral, PublicKeyToken=0dc50a750396c3ac. Additional information is below. : Value does not fall within the expected range.
I think this is a fairly generic error that is potentially caused many different ways. However, one simple explanation is that I’m referencing a field incorrectly. If the name of the field is "Due Date", I must reference it like this in an event receiver:
properties.ListItem["Due Date"]
When I misspell or use the wrong case when referencing the field, SharePoint generates the above mentioned runtime error. For example, this is wrong:
properties.ListItem["due Date"]
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I agree with paul but i also want to add something for this exception.
Sometime the Field Name is different than the Field Internal Name in the list so trying to access the field using Field Name in the object model gives us the above exception. To resolve this problem always try to access the fields using their Internal Names.
How can you find the internal Names of the Fields?
1) Go To Sharepoint List. Go to New | New Item.
2) New Item form will be displayed. Right click on the form and click on View Source. Search for the Field Internal Name in the opened HTML code. You will find the Field Internal Name along with Field Name.