Use types that are compatible with both 32 and 64 bit systems.
http://bugs.debian.org/614404 

http://www.zoneminder.com/forums/viewtopic.php?t=16060&highlight=discarding+packet+unrecognised+ssrc

Index: zoneminder/src/zm.h
===================================================================
--- zoneminder.orig/src/zm.h	2011-02-28 10:24:40.000000000 -0800
+++ zoneminder/src/zm.h	2011-02-28 10:28:51.000000000 -0800
@@ -17,6 +17,8 @@
 // Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA  02111-1307, USA.
 // 
 
+#include "stdint.h"
+
 #ifndef ZM_H
 #define ZM_H
 
@@ -34,14 +36,14 @@
 #endif
 }
 
-typedef unsigned char       U8;
-typedef unsigned short      U16;
-typedef unsigned long       U32;
-typedef unsigned long long  U64;
-
-typedef signed char         S8;
-typedef signed short        S16;
-typedef signed long         S32;
-typedef signed long long    S64;
+typedef uint8_t             U8;
+typedef uint16_t            U16;
+typedef uint32_t            U32;
+typedef uint64_t            U64;
+
+typedef int8_t              S8;
+typedef int16_t             S16;
+typedef int32_t             S32;
+typedef int64_t             S64;
 
 #endif // ZM_H
