In Excel file Data Insertion Problem

The link you are refering to, is about 256 columns and not characters. The 256 characters problem is described here with a workaround: http://support.microsoft.com/kb/213841

For more detail have a look of the link

http://forums.asp.net/t/1160369.aspx?The+field+is+too+small+to+accept+the+amount+of+data+you+attempted+to+add+Try+inserting+or+pasting+less+data+

http://forums.asp.net/t/1555208.aspx?The+field+is+too+small+to+accept+the+amount+of+data+you+attempted+to+add+Try+inserting+or+pasting+less+data+

https://support.microsoft.com/en-in/kb/896950