KDEINIT cannot launch anything! (...after some inactivity)

If I leave my computer sitting awhile (I'm guessing 30 minutes, but haven't timed it) and then come back to it, KDE has problems launching programs from either the panel buttons or my keyboard's multimedia keys. In some cases, I'll get the bouncing cursor and the taskbar will show the name of the program that's trying to launch, but it will never actually launch. In other cases, I get a message box saying "KDEINIT could not launch [whatever program]." The behavior seems dependent on the program that's trying to start--Iceweasel (Firefox) exhibits the first behavior, while Konqueror exhibits the second.

I suspect it's also affecting my monitor's power management, since sometimes it doesn't go to suspend or power off, even though the Control Center has times set for both.

The only remedy I've come across is to log out of and back into KDE, which I'd prefer not to have to do. I've searched a couple of times now for hints on why KDE might do this, but only come up with things that affect one application at a time (and usually involve desktop shortcuts requiring root access).

FWIW, I'm running Debian Testing, with KDE 3.5.5.

Yesterday I tried re-installing everything related to KDE, to no avail. I did run across one more clue, which is that each time I try to launch a program, one of the following two errors gets added to my .xsession-errors file:

Code:

---

Xlib: connection to ":0.0" refused by server
Xlib: Invalid MIT-MAGIC-COOKIE-1 key
Xlib: connection to ":0.0" refused by server
Xlib: Invalid MIT-MAGIC-COOKIE-1 key

(firefox-bin:14938): Gtk-WARNING **: cannot open display:

---

The above is all generated by trying to launch Firefox from my keyboard's multi-media key.

Code:

---

Xlib: connection to ":0.0" refused by server
Xlib: Invalid MIT-MAGIC-COOKIE-1 key
Xlib: connection to ":0.0" refused by server
Xlib: Invalid MIT-MAGIC-COOKIE-1 key
konsole: cannot connect to X server :0.0
X Error: BadWindow (invalid Window parameter) 3
  Major opcode:  19
  Minor opcode:  0
  Resource id:  0xc008e9
X Error: BadWindow (invalid Window parameter) 3
  Major opcode:  20
  Minor opcode:  0
  Resource id:  0xc008e9

---

The above is what I get when trying to launch Konsole, again from a multi-media key.

I get the same error in .xsession-errors for Firefox when trying to launch it from my panel, and trying to launch Konsole from the K-menu entry gives the same errors except for the BadWindow bits (which I think are related to the dialog that pops up to tell me Kdeinit could not launch konsole).

Googling for these new clues again turns up nothing relevant; everything related to not being able to connect to the X server appears to be an xhosts and su thing, which is not my problem (I'm assuming) because I'm trying to run things as myself on my own X server--things which had worked fine earlier in the same session.

Any hints on what to check?

Someone in the Salt Lake Linux Users Group pointed me in the right direction. My ~/.Xauthority was getting changed, as shown in the output of 'xauth list :0' before and after the problem. I determined that it was changing when I connected using ssh from my laptop, with X forwarding. From what I can gather, the problem probably stems from a misconfigured hostname on one or both machines, but I haven't found what I'm supposed to do about that. In the meantime, this page gave me a hint about altering sshd_config to change how ssh looks at hostnames. So I added the line 'X11UseLocalhost no' and now it works fine.