Possibly because of this:

You will need to enable it, and restart the instance. After...

Is the database being replicated? The log can't be cleared until any transactions have been replicated.

If you don't care about the performance of the archiving routine, then do it one row at a time.

Get a list of the rows to be archived into a temp...

You may also want to take a look at your Distribution Agent Profile.

The default profile will try to apply 100 publisher transactions before issuing a commit at the subscriber. Therefore...

You've got an erroneous line with '177' half way down the code you posted.

That should work... are you sure the transaction log backup file actually has a backup of the original forms database?

Run a restore of the log with headeronly to verify.

RESTORE HEADERONLY...

I would start off with SQL Profiler, and profile execution of the stored procedure at the statement level to try and identify the actual statement that is causing the exception.

At a guess, unless you are terminating rows with just a carriage return instead of a carriage return and line feed, the last line of your format file should read...

Have you run a full backup at any time?

Differential backups will only run if you've done a full backup, as they only back up changes made since the last...

It will delete both.

The parameter you are passing to sp_delete_backuphistory is telling it to delete ALL backup history OLDER than that date.

The behaviour you are seeing will be caused by different settings between VS2010 and SSMS for the "CONCAT_NULL_YIELDS_NULL" connection setting.

You should still see the output from select @sql even with the display of the out params.

The fact that you can't see anything would lead me to...

OK, but when running the procedure in SSMS, does it generate the same...

Do you end up with the same command if you run it in SSMS instead of the debugger?

One thing that doesn't look right... you have declared @YYYYMMDD as CHAR(10), but...

Start off by replacing the EXECUTE (@Sql) with PRINT @sql so you can see the exact command you have generated.