Good to know you solved your problem.
As for the Arithmethic Exception error, that's a known issue: old password authentication support was dropped in Connector/NET 6.6
As stated in this bug report
http://bugs.mysql.com/bug.php?id=66647, that steps to reproduce it (and fix it) are:
Create a user with old style authentication, using these SQL as sample:
create user 'oldpassuser'@'localhost'
grant all on *.* to 'oldpassuser'@'localhost'
set password for 'oldpassuser'@'localhost' = old_password( '123' )
Then try to connect with that user in Connector/NET 6.6.2 or later. You will get the "Arithmetic operation resulted in overflow" error.
Now try this SQL to reset the password to the 4.1 authentication style
set password for 'oldpassuser'@'localhost' = password( '123' )
This assumes that the server variable old_passwords must be 0 (1 means using old passowrds).
Connect again with same credentials in Connector/NET 6.6.x, you will have no problem.
(What is definitely missing, and will add in a future version is a more friendly error, stating that problem is effective old password not supported).
Thanks.