Question

    Threads 
------- 
ThreadID
 UsersID 
Date 
ThreadTitle
 ThreadParagraph 
ThreadClosed 

  Topics 
-----
 TopicsID 
Theme
 Topics 
Date 

Here is my statement:

  StringBuilder insertCommand = new StringBuilder();
    insertCommand.Append("DECLARE @TopicsID int");
    insertCommand.Append("INSERT INTO Topics(Theme,Topics,Date)");
    insertCommand.Append("VALUES(@topic,@subTopic,GETDATE())");
    insertCommand.Append("SET @TopicsID = SCOPE_IDENTITY()");

    insertCommand.Append("INSERT INTO Threads(UsersID,TopicsID,Date,ThreadTitle,ThreadParagraph,ThreadClosed)");
    insertCommand.Append("VALUES(@uniqueIdentifier,@TopicsID,GETDATE(),@questionTitle,@questionParagraph,0)");

I get this:

Incorrect syntax near the keyword
‘INTO’. Must declare the scalar
variable “@TopicsID”. Must declare the
scalar variable “@TopicsID”.

Answer 1

Try
insertCommand.AppendLine

SQL sees

DECLARE @TopicsID intINSERT INTO Topics(Theme,Topics,Date) ...

You need to separate the distinct statements