Connectionstring for ADODB Connection is OK.
Provider=SQLOLEDB.1;Persist Security Info=False;User ID=DOC2PDFADMIN;Password=doc2pdfadmin;Initial Catalog=DOC2PDFPRD;Data Source=YOURDBSERVER

But if connectionstring for SqlConnection is not OK.
Persist Security Info=False;Integrated Security=SSPI;UID=DOC2PDFADMIN;PWD=doc2pdfadmin;Initial Catalog=DOC2PDFQAS;Data Source=YOURDBSERVER

it will report login failed for MACHINE\USER.

Refer ：http://msdn.microsoft.com/zh-cn/library/system.data.sqlclient.sqlconnection.connectionstring%28VS.80%29.aspx

Connectionstring of ADODB Connection and SqlConnection