"This operation requires a connection to the 'master' database. Unable to create a connection to the 'master' database because the original database connection has been opened and credentials have been removed from the connection string. Supply an unopened connection."

I had this error and solved it by adding "Persist Security Info=true" to the connection string.

意思是在连接字符串上要加 Persist Security Info=true

Persist Security Info=true 的意思是让.net一直保存着连接密码，默认是为false的

只是不明白 为什么在出现一次错误后 第二次就不会出现 难道出现过错误 .net就自动把密码给保存上了？