I have just updated my Slackware-current installation. My last updated was on 2020-11-21. Something in between made gkrellm start to crash for some themes. For 3 themes, gkrellm works just fine. For other 3 themes (the dark ones) it is crashing with the message:

The program 'gkrellm' received an X Window System error.
This probably reflects a bug in the program.
The error was 'BadPixmap (invalid Pixmap parameter)'.
(Details: serial 9342 error_code 4 request_code 56 minor_code 0)
(Note to programmers: normally, X errors are reported asynchronously;
that is, you will receive the error a while after causing it.
To debug your program, run it with the --sync command line
option to change this behavior. You can then get a meaningful
backtrace from your debugger if you break on the gdk_x_error() function.)

I have no idea where to look for the error.
Any help is appreciated!
Thanks.

If the themes in question use transparency it's a known issue, which unfortunately is unlikely to be fixed. I'm going to miss gkrellm when I move to slackware 15.0, but I can't live without transparency.

I cycled thru every theme I have installed with GKrellM, none of them cause a crash.

I'm on the same ChangeLog.txt Mon Jan 11 19:51:04 UTC 2021

Slackware64-current Plasma

I should have added this is with xfce4 4.16 which doesn't draw the desktop to the root window apparently.

Forgot to say; I am on Xfce.
Sorry.

So it seems the problem is with the changes made in xfce4 4.16!?
Some internal changes have dissatisfied many people. I start to understand why...