Neverball works, which is as far as I know an OpenGL application, glxgears works, no errors or warnings at all.
However, Unreal Tournament 2004 does not work, and Open Arena does not work. The former, Unreal Tournament worked before, then suddenly stopped working one day, I ignored it and thought it had to be some bug in UT since Neverball still worked. But then I wanted to test Open Arena, which gives the same errors as UT does:

Open Arena:

"
...loading libGL.so.1:
Calling SDL_Init(SDL_INIT_VIDEO)...
SDL_Init(SDL_INIT_VIDEO) passed.
QGL_Init: Can't load libGL.so.1 from /etc/ld.so.conf or current dir:
failed
----- CL_Shutdown -----
RE_Shutdown( 1 )
-----------------------
Sys_Error: GLimp_Init() - could not load OpenGL subsystem
"

UT:

"
Could not load OpenGL library

History:

Exiting due to error
"

I attempted to copy the demanded file into the current directory, but to no avail -- same error.

An strace of both applications show that both load the file "libGL.so.1" with an open() call which ends in success. Despite this Open Arena claims to be unable to load the very same file it actually loads with no problem at all, UT also fails, and I assume this is due to the same problem as Open Arena?

I'm unable to discern from the strace what exactly is the problem -- why Open Arena fails to work -- my own private small OpenGL coding projects compile and execute with no known issue(s) as well.

This system is an x86 computer (AMD X2 3800+, 1 GiB, Nvidia 7800 GT), running GNU/Linux Slackware.

bash-3.1$ cat /etc/slackware-version
Slackware 11.0.0
bash-3.1$ uname -a
Linux x86_1 2.4.33.3 #1 Fri Sep 1 01:48:52 CDT 2006 i686 athlon-4 i386 GNU/Linux

From glxinfo: "server glx vendor string: NVIDIA Corporation"
glxgears executes at > 13 000 FPS.

I have no other issues that I know about on my system.

Here is an extract of the strace for Open Arena:

open("/usr/local/openarena-0.7.0/libGL.so.1", O_RDONLY) = 13
read(13, "\177ELF\1\1\1\0\0\0\0\0\0\0\0\0\3\0\3\0\1\0\0\0\0 \3\3\000"..., 512) = 512
fstat64(13, {st_mode=S_IFREG|0755, st_size=601272, ...}) = 0
mmap2(NULL, 605568, PROT_READ|PROT_EXEC, MAP_PRIVATE|MAP_DENYWRITE, 13, 0) = 0x45d6a000
mmap2(0x45de2000, 110592, PROT_READ|PROT_WRITE|PROT_EXEC, MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 13, 0x77) = 0x45de2000
mmap2(0x45dfd000, 3456, PROT_READ|PROT_WRITE|PROT_EXEC, MAP_PRIVATE|MAP_FIXED|MAP_ANONYMOUS, -1, 0) = 0x45dfd000
close(13) = 0
open("/etc/ld.so.cache", O_RDONLY) = 13
fstat64(13, {st_mode=S_IFREG|0644, st_size=133341, ...}) = 0
mmap2(NULL, 133341, PROT_READ, MAP_PRIVATE, 13, 0) = 0x45d3b000
close(13)
open("/usr/lib/libGLcore.so.1", O_RDONLY) = 13
read(13, "\177ELF\1\1\1\0\0\0\0\0\0\0\0\0\3\0\3\0\1\0\0\0\2 00\301"..., 512) = 512
fstat64(13, {st_mode=S_IFREG|0755, st_size=9916028, ...}) = 0
mmap2(NULL, 9897696, PROT_READ|PROT_EXEC, MAP_PRIVATE|MAP_DENYWRITE, 13, 0) = 0x45dfe000
mmap2(0x46733000, 225280, PROT_READ|PROT_WRITE|PROT_EXEC, MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 13, 0x934) = 0x46733000
mmap2(0x4676a000, 18144, PROT_READ|PROT_WRITE|PROT_EXEC, MAP_PRIVATE|MAP_FIXED|MAP_ANONYMOUS, -1, 0) = 0x4676a000
close(13) = 0
open("/usr/lib/tls/libnvidia-tls.so.1", O_RDONLY) = 13
read(13, "\177ELF\1\1\1\0\0\0\0\0\0\0\0\0\3\0\3\0\1\0\0\0P\ 4\0\000"..., 512) = 512
lseek(13, 1300, SEEK_SET) = 1300
read(13, "\4\0\0\0\20\0\0\0\1\0\0\0GNU\0\0\0\0\0\2\0\0\0\3\ 0\0\0"..., 32) = 32
fstat64(13, {st_mode=S_IFREG|0755, st_size=2324, ...}) = 0
close(13) = 0
munmap(0x45d3b000, 133341) = 0
munmap(0x45d6a000, 60556 = 0
munmap(0x45dfe000, 9897696) = 0
write(2, "QGL_Init: Can\'t load libGL.so.1 "..., 70) = 70
write(2, "failed\n", 7)
gettimeofday({1186107143, 928166}, NULL) = 0
write(2, "----- CL_Shutdown -----\n", 24) = 24
open("/home/pango/.openarena/qkey", O_RDONLY) = 13
fstat64(13, {st_mode=S_IFREG|0644, st_size=2048, ...}) = 0
mmap2(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x40037000
_llseek(13, 0, [0], SEEK_CUR) = 0
fstat64(13, {st_mode=S_IFREG|0644, st_size=2048, ...}) = 0
_llseek(13, 0, [0], SEEK_SET) = 0
read(13, "0T\257\225e\210\3256O\341\253\370\374+\260\261\24 7h\16"..., 204 = 2048
_llseek(13, 2048, [2048], SEEK_SET) = 0
close(13) = 0
munmap(0x40037000, 4096) = 0
open("/home/pango/.openarena/qkey", O_RDONLY) = 13
fstat64(13, {st_mode=S_IFREG|0644, st_size=2048, ...}) = 0
mmap2(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x40037000
_llseek(13, 0, [0], SEEK_CUR) = 0
fstat64(13, {st_mode=S_IFREG|0644, st_size=2048, ...}) = 0
_llseek(13, 0, [0], SEEK_SET) = 0
read(13, "0T\257\225e\210\3256O\341\253\370\374+\260\261\24 7h\16"..., 204 = 2048
_llseek(13, 2048, [2048], SEEK_SET) = 0
close(13) = 0
munmap(0x40037000, 4096) = 0
write(2, "RE_Shutdown( 1 )\n", 17) = 17
write(2, "-----------------------\n", 24) = 24
fcntl64(0, F_GETFL) = 0x8002 (flags O_RDWR|O_LARGEFILE)
fcntl64(0, F_SETFL, O_RDWR|O_LARGEFILE) = 0
write(2, "Sys_Error: GLimp_Init() - could "..., 59) = 59
exit_group(1) = ?