Noticed that this problem was already reported in the tech support forum on Windows and Mac. It seems to be happening on Linux as well.
Bitcoin version 0.6.2
OS: Linux Bart 3.2.0-24-generic #37-Ubuntu SMP Wed Apr 25 08:43:22 UTC 2012 x86_64 x86_64 x86_64 GNU/Linux
fglrxinfo: display: :0 screen: 0
OpenGL vendor string: Advanced Micro Devices, Inc.
OpenGL renderer string: AMD Radeon HD 6800 Series
OpenGL version string: 4.2.11631 Compatibility Profile Context
Diablo Verion - May 11, 2012
Diablo invocation command and output (verified that user credentials and port number are correct for bitcoin -daemon)
urt@Bart:~/bin/Diablo$ ./DiabloMiner-Linux.sh -l http://api2.bitcoin.cz
-u xxxxxx -p xxxxxx -D 1
[5/19/12 11:29:35 AM] Started
[5/19/12 11:29:35 AM] Connecting to: http://api2.bitcoin.cz:8332/
[5/19/12 11:29:35 AM] Using AMD Accelerated Parallel Processing OpenCL 1.2 AMD-APP (923.1)
[5/19/12 11:29:37 AM] BFI_INT patching enabled, disabling hardware check errors
[5/19/12 11:29:37 AM] Added Barts (#1) (14 CU, local work size of 256)
mhash: 267.6/267.7 | accept: 0 | reject: 0 | hw error: 0
The accept count never changes - I've left it running overnight with no success. I have another miner running on Windows 7 on a different machine (Radeon HD5800) also using Slush's pool with Phoenix. It works fine.