INSERT Query SQL (Error converting data type nvarchar to (null))

I'm trying to run an INSERT query but it asks me to convert varchar to null. Here's the code:

INSERT Runtime.dbo.History (DateTime, TagName, vValue)
VALUES ('2015-09-10 09:00:00', 'ErrorComment', 'Error1')

Error message:

Error converting data type nvarchar to (null).

The problem is at the vValue column.

column vValue(nvarchar, null) 

How it looks in the database:

The values inside vValue are placed by the program I'm using. I'm just trying to manually insert into the database.

Last post was with the wrong column, I apologize.

After contacting Wonderware support i found out that INSERT is not supported on the vValue column by design. It’s a string value and updates are supposed to carry out via the StringHistory table.