I download the client for linux (running Slackware 13.37 64 bits) and when i run the executable i get this message:

bash-4.1$ ./swekey-client --list
./swekey-client: /usr/lib64/libcurl.so.4: no version information available (required by ./swekey-client)

Reference URL's:
http://www.swekey.com
http://developer.swekey.com/

What's the output of It should be a link to something like libcurl.so.4.2.0. Is that correct?
ciao,
jdk

bash-4.1$ ls -l /usr/lib64/libcurl.so.4
lrwxrwxrwx 1 root root 16 May 6 09:32 /usr/lib64/libcurl.so.4 -> libcurl.so.4.2.0

bash-4.1$ ls -hal | grep url
-rw-r--r-- 1 root root 662K Mar 29 13:36 libcurl.a
-rwxr-xr-x 1 root root 1.1K Mar 29 13:36 libcurl.la
lrwxrwxrwx 1 root root 16 May 6 09:32 libcurl.so -> libcurl.so.4.2.0
lrwxrwxrwx 1 root root 16 May 6 09:32 libcurl.so.4 -> libcurl.so.4.2.0
-rwxr-xr-x 1 root root 353K Mar 29 13:36 libcurl.so.4.2.0

bash-4.1$ ldd swekey-client
./swekey-client: /usr/lib64/libcurl.so.4: no version information available (required by ./swekey-client)
linux-vdso.so.1 => (0x00007ffff1933000)
libusb-0.1.so.4 => /usr/lib64/libusb-0.1.so.4 (0x00007fc9f9bf5000)
libpthread.so.0 => /lib64/libpthread.so.0 (0x00007fc9f99d6000)
libcurl.so.4 => /usr/lib64/libcurl.so.4 (0x00007fc9f977e000)
libstdc++.so.6 => /usr/lib64/libstdc++.so.6 (0x00007fc9f947a000)
libm.so.6 => /lib64/libm.so.6 (0x00007fc9f91f4000)
libgcc_s.so.1 => /usr/lib64/libgcc_s.so.1 (0x00007fc9f8fdf000)
libc.so.6 => /lib64/libc.so.6 (0x00007fc9f8c39000)
libusb-1.0.so.0 => /usr/lib64/libusb-1.0.so.0 (0x00007fc9f8a2b000)
librt.so.1 => /lib64/librt.so.1 (0x00007fc9f8822000)
/lib64/ld-linux-x86-64.so.2 (0x00007fc9f9e32000)
libidn.so.11 => /usr/lib64/libidn.so.11 (0x00007fc9f85f0000)
libldap-2.4.so.2 => /usr/lib64/libldap-2.4.so.2 (0x00007fc9f83ab000)
libssl.so.0 => /usr/lib64/libssl.so.0 (0x00007fc9f8158000)
libcrypto.so.0 => /usr/lib64/libcrypto.so.0 (0x00007fc9f7dcf000)
libdl.so.2 => /lib64/libdl.so.2 (0x00007fc9f7bca000)
libz.so.1 => /usr/lib64/libz.so.1 (0x00007fc9f79b4000)
liblber-2.4.so.2 => /usr/lib64/liblber-2.4.so.2 (0x00007fc9f77a5000)
libresolv.so.2 => /lib64/libresolv.so.2 (0x00007fc9f758a000)
libsasl2.so.2 => /usr/lib64/libsasl2.so.2 (0x00007fc9f7371000)

Maybe running it through gdb might give you more information.
jdk

bash-4.1$ gdb swekey-client
GNU gdb (GDB) 7.2
Copyright (C) 2010 Free Software Foundation, Inc.
License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>
This is free software: you are free to change and redistribute it.
There is NO WARRANTY, to the extent permitted by law. Type "show copying"
and "show warranty" for details.
This GDB was configured as "x86_64-slackware-linux".
For bug reporting instructions, please see:
<http://www.gnu.org/software/gdb/bugs/>...
Reading symbols from /home/ferdna/Downloads/swekey/swekeyclient/swekey-client...done.
(gdb) run --list
Starting program: /home/ferdna/Downloads/swekey/swekeyclient/swekey-client --list
/home/ferdna/Downloads/swekey/swekeyclient/swekey-client: /usr/lib64/libcurl.so.4: no version information available (required by /home/ferdna/Downloads/swekey/swekeyclient/swekey-client)
[Thread debugging using libthread_db enabled]

Program exited normally.
(gdb)

I emailed swekey support and they responded with:

It was compiled on debian 5

#ldd swekey-client
linux-vdso.so.1 => (0x00007fff3b9b7000)
libusb-0.1.so.4 => /lib/libusb-0.1.so.4 (0x00007f2544cd0000)
libpthread.so.0 => /lib/libpthread.so.0 (0x00007f2544ab3000)
libcurl.so.4 => /usr/lib/libcurl.so.4 (0x00007f254485a000)
libstdc++.so.6 => /usr/lib/libstdc++.so.6 (0x00007f2544554000)
libm.so.6 => /lib/libm.so.6 (0x00007f25442d1000)
libgcc_s.so.1 => /lib/libgcc_s.so.1 (0x00007f25440ba000)
libc.so.6 => /lib/libc.so.6 (0x00007f2543d37000)
/lib64/ld-linux-x86-64.so.2 (0x00007f2544ee9000)
libidn.so.11 => /usr/lib/libidn.so.11 (0x00007f2543b04000)
liblber-2.4.so.2 => /usr/lib/liblber-2.4.so.2 (0x00007f25438f5000)
libldap_r-2.4.so.2 => /usr/lib/libldap_r-2.4.so.2 (0x00007f25436aa000)
librt.so.1 => /lib/librt.so.1 (0x00007f25434a2000)
libgssapi_krb5.so.2 => /usr/lib/libgssapi_krb5.so.2 (0x00007f254326d000)
libssl.so.0.9.8 => /lib/libssl.so.0.9.8 (0x00007f254301b000)
libcrypto.so.0.9.8 => /lib/libcrypto.so.0.9.8 (0x00007f2542c8f000)
libz.so.1 => /lib/libz.so.1 (0x00007f2542a76000)
libresolv.so.2 => /lib/libresolv.so.2 (0x00007f254285d000)
libsasl2.so.2 => /usr/lib/libsasl2.so.2 (0x00007f2542642000)
libgnutls.so.26 => /usr/lib/libgnutls.so.26 (0x00007f25423a0000)
libkrb5.so.3 => /usr/lib/libkrb5.so.3 (0x00007f25420de000)
libk5crypto.so.3 => /usr/lib/libk5crypto.so.3 (0x00007f2541eb8000)
libcom_err.so.2 => /lib/libcom_err.so.2 (0x00007f2541cb3000)
libkrb5support.so.0 => /usr/lib/libkrb5support.so.0 (0x00007f2541aab000)
libdl.so.2 => /lib/libdl.so.2 (0x00007f25418a7000)
libkeyutils.so.1 => /lib/libkeyutils.so.1 (0x00007f25416a3000)
libtasn1.so.3 => /usr/lib/libtasn1.so.3 (0x00007f2541492000)
libgcrypt.so.11 => /lib/libgcrypt.so.11 (0x00007f2541219000)
libgpg-error.so.0 => /lib/libgpg-error.so.0 (0x00007f2541015000)

any ideas?