The following logs will help understand the problem better.

# cat marker_example.stp 
probe kernel.marker("subsystem_event") { printf("subsystem_event, hit\n") }
probe kernel.marker("subsystem_eventb") { printf("subsystem_eventb, hit\n") }

# stap -vvvv marker_example.stp 
SystemTap translator/driver (version 0.8/0.137 non-git sources)
Copyright (C) 2005-2008 Red Hat, Inc. and others
This is free software; see the source for copying conditions.
Session arch: i686 release: 2.6.27.5-41.fc9.i686
Created temporary directory "/tmp/stapdcGCir"
Searched '/usr/share/systemtap/tapset/i686/*.stp', found 2
Searched '/usr/share/systemtap/tapset/*.stp', found 43
Pass 1: parsed user script and 45 library script(s) in 290usr/0sys/295real ms.
semantic error: probe point mismatch at position 1 (alternatives:
function(number) function(string) mark(string) statement(number)
statement(string)): identifier 'kernel' at marker_example.stp:1:7 while
resolving probe point kernel.marker("subsystem_event")
        source: probe kernel.marker("subsystem_event") {
printf("subsystem_event, hit\n") }
                      ^
semantic error: probe point mismatch at position 1 (alternatives:
function(number) function(string) mark(string) statement(number)
statement(string)): identifier 'kernel' at :2:7 while resolving probe point
kernel.marker("subsystem_eventb")
        source: probe kernel.marker("subsystem_eventb") {
printf("subsystem_eventb, hit\n") }
                      ^
semantic error: no probes found
Pass 2: analyzed script: 0 probe(s), 0 function(s), 0 embed(s), 0 global(s) in
0usr/0sys/4real ms.
Pass 2: analysis failed.  Try again with more '-v' (verbose) options.
Running rm -rf /tmp/stapdcGCir

The behaviour shown above was seen on Fedora 9 and Fedora 10 distributions with
the bundled version of SystemTap.