clDevicesNum returned error, no GPUs usable I get this error with BFGMiner, when running "bfgminer -D -d?:"

 [2013-04-25 09:47:31] ft232r_scan: Found 093a:2510 - not a ft232r                    
 [2013-04-25 09:47:31] ft232r_scan: Found 1d6b:0002 - not a ft232r                    
 [2013-04-25 09:47:31] ft232r_scan: Found 1d6b:0002 - not a ft232r                    
 [2013-04-25 09:47:31] ft232r_scan: Found 8087:0020 - not a ft232r                    
 [2013-04-25 09:47:31] ft232r_scan: Found 8087:0020 - not a ft232r                    
 [2013-04-25 09:47:31] Started bfgminer 3.0.1                    
 [2013-04-25 09:47:31] Loaded configuration file /home/geremia/.bfgminer/bfgminer.conf                    
 [2013-04-25 09:47:31] CL Platform 0 vendor: Intel(R) Corporation                    
 [2013-04-25 09:47:31] CL Platform 0 name: Intel(R) OpenCL                    
 [2013-04-25 09:47:31] CL Platform 0 version: OpenCL 1.1 LINUX                    
 [2013-04-25 09:47:31] Error -1: Getting Device IDs (num)                    
 **[2013-04-25 09:47:31] clDevicesNum returned error, no GPUs usable**                    
 [2013-04-25 09:47:31] Not a ZTEX device 093a:2510                    
 [2013-04-25 09:47:31] Not a ZTEX device 1d6b:0002                    
 [2013-04-25 09:47:31] Not a ZTEX device 1d6b:0002                    
 [2013-04-25 09:47:31] Not a ZTEX device 8087:0020                    
 [2013-04-25 09:47:31] Not a ZTEX device 8087:0020                    
 [2013-04-25 09:47:31] Devices detected:                    
 [2013-04-25 09:47:31]   0. CPU 0  (driver: cpu)                    
 [2013-04-25 09:47:31]   1. CPU 1  (driver: cpu)                    
 [2013-04-25 09:47:31]   2. CPU 2  (driver: cpu)                    
 [2013-04-25 09:47:31]   3. CPU 3  (driver: cpu)                    
 4 devices listed

Here is my output of "lspci -nn | grep VGA":

00:02.0 VGA compatible controller [0300]: Intel Corporation Core Processor Integrated Graphics Controller [**8086:0046**] (rev 18)

Can I not mine with an Intel Integrated Graphics Controller? thanks
Bitcoin mining is principally an integer maths task, not a graphics task.  It just so happens that the hundreds of processors found on modern graphics cards can sometimes be suitable for parallel calculation of the bitcoin task, at upwards of a hundred times the best available rate from four cpu calculations.

See wiki reports on bitcoin hardware for comparison figures.

Unfortunately for you, Intel copied some parts of modern GPU designs into their system on a chip, but to save money they left out some transistors here and there which might not get used in direct X 11 graphics but would be necessary for parallel calculations for bitcoin.

So, you have on-chip graphics suitable for screen display and a few other specifically graphics tasks, but you do not have a general purpose massively parallel GPU for bitcoin calculations.

The error message "clDevicesNum returned error, no GPUs usable" appears on one of my systems which does have a suitable graphics card for bitcoin mining and does find openCL drivers for it when configured before compile.  I'm trying to find out what is incorrect in my configuration.