ORA-00911: invalid character in C#, but not Oracle SQL Developer

At a minimum, you don't want the trailing semicolon in the SQL statement you send from C#.

I would strongly advocate as well that you use bind variables rather than concatenating together a string with your SQL statement. That will be more efficient, it will prevent shared pool related errors, it will make your DBA much happier, and it will protect you against SQL injection attacks.

Had the same problem, if anyone else is struggling with this issue try the following:

Remove the ";" from the sqlSentence String in Visual Studio. The ";" is just part of the Oracle DBmanager to separate sentences, it doesn't work out of there (it gets recognized as an invalid character)