Default printer problem

[Gil]

A problem just appeared, my chosen default printer will no longer be a
default after a system startup, and there will be no default. If I
change it's sharing status (on or off) it will get the default checkmark
back. Also, when it is not shown as default Firefox will complain that
there is no printer attached.
I have a Canon i850 printer connected to my system, which is my default,
in addition to a Epsom EPSON Stylus CX9400Fax, and one other printer
attached to another computer on the network, The only recent addition
is the CX9400. I have uninstalled and reinstalled the i850 to no
effect, when I restart there is no default printer. Any suggestions?

XP Pro with SP2
BFG nForce 650i Ultra Socket 775 BFGINF650IU MB
Intel Pentium D 805 Dual Core
2Gb 2x Ultra 1024MB PC4200 DDR2 533MHz
XFX GeForce 6200 video

 

[Gil]

A problem just appeared, my chosen default printer will no longer be a
default after a system startup, and there will be no default. If I
change it's sharing status (on or off) it will get the default checkmark
back. Also, when it is not shown as default Firefox will complain that
there is no printer attached.
I have a Canon i850 printer connected to my system, which is my default,
in addition to a Epsom EPSON Stylus CX9400Fax, and one other printer
attached to another computer on the network, The only recent addition
is the CX9400. I have uninstalled and reinstalled the i850 to no
effect, when I restart there is no default printer. Any suggestions?

XP Pro with SP2
BFG nForce 650i Ultra Socket 775 BFGINF650IU MB
Intel Pentium D 805 Dual Core
2Gb 2x Ultra 1024MB PC4200 DDR2 533MHz
XFX GeForce 6200 video

Addendum
I find I cannot print from any application, using any printer, until I
have toggled some setting, for instance sharing.

I have done a repair installation of XP, including all the updates, and
the problem persists.