Error installing mongrel:

Hello, I am currently not able to instal mongrel, I run a Linux Ubuntu 10.04 system with Gems 1.3.7 when I do a "sudo gem install mongrel" I get this sequence of messages:
luisflores@luisflores-laptop:~$ sudo gem install mongrel
Building native extensions. This could take a while...
ERROR: Error installing mongrel:

ERROR: Failed to build gem native extension.

/usr/local/bin/ruby extconf.rb checking for main() in -lc... yes
creating Makefile

make
gcc -I. -I/usr/local/include/ruby-1.9.1/i686-linux -I/usr/local/include/ruby-1.9.1/ruby/backward -I/usr/local/include/ruby-1.9.1 -I. -D_FILE_OFFSET_BITS=64 -fPIC -O3 -ggdb -Wextra -Wno-unused-parameter -Wno-parentheses -Wpointer-arith -Wwrite-strings -Wno-missing-field-initializers -Wno-long-long -o http11.o -c http11.c
http11.c: In function ‘http_field’:
http11.c:70: warning: format not a string literal and no format arguments
http11.c:71: warning: format not a string literal and no format arguments
http11.c:77: error: ‘struct RString’ has no member named ‘ptr’
http11.c:77: error: ‘struct RString’ has no member named ‘len’
http11.c: In function ‘request_uri’:
http11.c:102: warning: format not a string literal and no format arguments
http11.c: In function ‘fragment’:
http11.c:113: warning: format not a string literal and no format arguments
http11.c: In function ‘request_path’:
http11.c:124: warning: format not a string literal and no format arguments
http11.c: In function ‘query_string’:
http11.c:135: warning: format not a string literal and no format arguments
http11.c: In function ‘header_done’:
http11.c:172: error: ‘struct RString’ has no member named ‘ptr’
http11.c:172: error: ‘struct RString’ has no member named ‘ptr’
http11.c:172: error: ‘struct RString’ has no member named ‘ptr’
http11.c:174: error: ‘struct RString’ has no member named ‘ptr’
http11.c:176: error: ‘struct RString’ has no member named ‘ptr’
http11.c:177: error: ‘struct RString’ has no member named ‘len’
http11.c: In function ‘HttpParser_execute’:
http11.c:298: error: ‘struct RString’ has no member named ‘ptr’
http11.c:299: error: ‘struct RString’ has no member named ‘len’
http11.c:307: warning: format not a string literal and no format arguments
make: *** [http11.o] Error 1

Gem files will remain installed in /usr/local/lib/ruby/gems/1.9.1/gems/mongrel-1.1.5 for inspection.
Results logged to /usr/local/lib/ruby/gems/1.9.1/gems/mongrel-1.1.5/ext/http11/gem_make.out

Would you please help me?
Thank you in advance for your valuable time.
Fernando Flores