I have the same problem. CCleaner Portable won't start (no CCleaner window appears), I just see in the task manager that there is a task called CCleaner.
The same problem is with version 6.04.10044, which was working without problems until three weeks ago.
I run CCleaner as administrator.
Windows 10 x64 22H2 with all system updates in the month of November.
I have ESET Internet Security 16.0.24.0 antivirus.
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I wouldn't have thought this installation/permissions situation would apply to the Portable which isn't installed.
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Having said that we have recently seen some users who are using the Portable from the C: drive rather than as actually portable.
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Are you running the Portable from a USB stick?
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Yes, indeed, CCleaner portable 6.06.10144 and older runs normally from a USB flash drive.
When a new version of CCleaner comes out, I always download the new portable version to the system C:\ drive and try it from there first, and if everything is fine, save it to a USB flash drive and use CCleaner portable from there normally.Since I couldn't run CCleaner portable from the C:\ drive, I didn't try again from the USB flash drive...
Thanks for comfirming that the Portable runs as normal if used as it's meant to be - from a USB stick.
(I'm not sure if that is now intentional to prevent people running it from the C: drive rather than installing CCleaner like they should? But it might well be).