This issue occurs on a Windows 7 system, updated to the last available Updates.

Classic Shell is installed on the host.

There is no antivirus or anti-malware.

The BOINC Manager is 7.20.2 (x64).

The client version is 7.20.2 for windows_x86_64

The sole project on the system is Primegrid.

BOINC is not installed as a service.

Autoruns reports that Windows starts 2 BOINC items from

  HKLM/SOFTWARE/Microsoft/Windows/CurrentVersion/Run
    c:\program files\boinc\boincmgr.exe
    c:\program files\boinc\boinctray.exe

BOINC CPU computation runs normally and as expected.

The problem is that BOINC does not find the GPU as an OpenCL device.

The GPU is a Radeon HD5850 which was previously used as a BOINC computing device. The HD5850 was replaced with a Radeon HD6570 which was used for about a year. When the HD5850 was reinstalled earlier this week, BOINC did not see it as an OpenCL compliant GPU.

The Windows GPU driver is official AMD, 15.301.1901.0 of 2/26/2016 which is the last official release for the HD5850. There are no issues with the graphics and the GPU passes the DirectX diagnostic.

GPU Caps Viewer 1.58.01 reports no OpenCL device except for the CPU.

The AMD APP SDK 3.0 was installed in the hope of solving the issue. It did not produce any noticeable changes.

Below is the BOINC startup log:

3/4/2023 7:03:52 PM |  | Starting BOINC client version 7.20.2 for windows_x86_64
3/4/2023 7:03:52 PM |  | Libraries: libcurl/7.84.0-DEV Schannel zlib/1.2.12
3/4/2023 7:03:52 PM |  | Data directory: C:\ProgramData\BOINC
3/4/2023 7:03:52 PM |  | Running under account Windows User
3/4/2023 7:03:52 PM |  | CAL: ATI GPU 0: ATI Radeon HD 5800/5900 series (Cypress/Hemlock) (CAL version 1.4.1848, 1024MB, 991MB available, 4176 GFLOPS peak)
3/4/2023 7:03:52 PM |  | App version needs OpenCL but GPU doesn't support it
3/4/2023 7:03:52 PM | PrimeGrid | Application uses missing ATI GPU
3/4/2023 7:03:52 PM |  | App version needs OpenCL but GPU doesn't support it
3/4/2023 7:03:52 PM | PrimeGrid | Application uses missing ATI GPU
3/4/2023 7:03:52 PM |  | All projects have zero resource share; setting to 100
3/4/2023 7:03:52 PM |  | Windows processor group 0: 4 processors
3/4/2023 7:03:52 PM |  | Host name: Workstation
3/4/2023 7:03:52 PM |  | Processor: 4 GenuineIntel Intel(R) Core(TM)2 Quad CPU Q9550 @ 2.83GHz [Family 6 Model 23 Stepping 10]
3/4/2023 7:03:52 PM |  | Processor features: fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov pat pse36 clflush dts acpi mmx fxsr sse sse2 ss htt tm pni ssse3 cx16 sse4_1 syscall nx lm vmx smx tm2 pbe
3/4/2023 7:03:52 PM |  | OS: Microsoft Windows 7: Professional x64 Edition, Service Pack 1, (06.01.7601.00)
3/4/2023 7:03:52 PM |  | Memory: 5.99 GB physical, 11.98 GB virtual
3/4/2023 7:03:52 PM |  | Disk: 185.71 GB total, 142.77 GB free
3/4/2023 7:03:52 PM |  | Local time is UTC -6 hours
3/4/2023 7:03:52 PM |  | No WSL found.
3/4/2023 7:03:52 PM | PrimeGrid | General prefs: from PrimeGrid (last modified 16-Sep-2022 18:53:53)
3/4/2023 7:03:52 PM | PrimeGrid | Host location: none
3/4/2023 7:03:52 PM | PrimeGrid | General prefs: using your defaults
3/4/2023 7:03:52 PM |  | Reading preferences override file
3/4/2023 7:03:52 PM |  | Preferences:
3/4/2023 7:03:52 PM |  | max memory usage when active: 3066.29 MB
3/4/2023 7:03:52 PM |  | max memory usage when idle: 3066.29 MB
3/4/2023 7:03:52 PM |  | max disk usage: 4.50 GB
3/4/2023 7:03:52 PM |  | suspend work if non-BOINC CPU load exceeds 50%
3/4/2023 7:03:52 PM |  | (to change preferences, visit a project web site or select Preferences in the Manager)
3/4/2023 7:03:52 PM |  | Setting up project and slot directories
3/4/2023 7:03:52 PM |  | Checking active tasks
3/4/2023 7:03:52 PM | PrimeGrid | Task llrPSP_446104789_0 is 9.89 days overdue; you may not get credit for it.  Consider aborting it.
3/4/2023 7:03:52 PM | PrimeGrid | URL http://www.primegrid.com/; Computer ID 1022621; resource share 100
3/4/2023 7:03:52 PM |  | Setting up GUI RPC socket
3/4/2023 7:03:52 PM |  | Checking presence of 25 project files

I have researched the "App version needs OpenCL but GPU does not support it" and "Application uses missing ATI GPU" messages. Several commentaries were found but none of them were directly applicable to this case (e.g., linux hosts, Windows 10, etc.)

If anyone can shed light on this issue I shall be grateful. The most common commentary from the internet in similar cases was essentially "yank out all AMD drivers using the AMD removal tool, pull out the APP SDK (and other issues) and see if that helps." I believe it would be quicker to reload Windows than to roll those dice, but I don't like the odds on either approach.

Final note: I seem to recall an issue with BOINC about three years back related to GPU detection, around release 7.2. Later releases did not detect GPUs properly. I have not investigated this.
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GPU Caps Viewer 1.58.01 reports no OpenCL device except for the CPU.

When another application reports it cannot find an OpenCL capable GPU either, it's drivers. Using last available drivers doesn't mean they include OpenCL for your device.

Always clean install drivers, don't use drivers of a previously installed video card. Use DDU in Windows Safe Mode to remove all previous driver remnants.

The proposed solution is correct. I removed the previous drivers with DDU, rebooted and then installed the latest Catalyst-compliant driver.