I have the same problem in a server with SQL 2000. But the code works fine in SQL 2005. One solution may be to replace the table variable by a temporary table (#InputBuffer instead @InputBuffer).

I had 2 minor problems too, here are (and his solution):

1.

...ON P.sid = L.sid

My server is in case sensitive mode, the alias is L, not l

2.

... OR P.program_name LIKE 'SQL Query Analyzer%'

In the original code appears "Analiser"

Hope be useful