I'm unable to build slony on an RHEL 5.3 machine. 

Running configure complains that my version of flex/lex is 'too old'. Checking the configure script, I see that it's trying match my flex version string (2.5.4) against this: 

if echo "$pgac_flex_version" | sed 's/[.a-z]/ /g' | awk '{ if ($1 = 2 && $2 = 5 && $3 >= 31) exit 0; else exit 1;}'

Configuration runs to completion despite the warning message. 

Then, during make/make all, I get the following errors: 

--------------------------------
Missing flex scan.l scan.c
gcc -g -O2 -Wall -Wmissing-prototypes -Wmissing-declarations -I../.. -DPGSHARE="\"/usr/local/postgresql/9.0.1/share/\""  -I/usr/local/postgresql/9.0.1/include/ -I/usr/local/postgresql/9.0.1/include/server/  -c -o parser.o parser.c
gcc -g -O2 -Wall -Wmissing-prototypes -Wmissing-declarations -I../.. -DPGSHARE="\"/usr/local/postgresql/9.0.1/share/\""  -I/usr/local/postgresql/9.0.1/include/ -I/usr/local/postgresql/9.0.1/include/server/  -c -o scan.o scan.c
gcc: scan.c: No such file or directory
gcc: no input files
make[2]: *** [scan.o] Error 1
make[2]: Leaving directory `/usr/src/slony1-2.0.5/src/slony_logshipper'
make[1]: *** [all] Error 2
make[1]: Leaving directory `/usr/src/slony1-2.0.5/src'
make: *** [all] Error 2
--------------------------------

[root@dbdev slony1-2.0.5]# cat /etc/redhat-release 
Red Hat Enterprise Linux Server release 5.3 (Tikanga)

Please let me know if you need any other info from me.