I am having a similar issue but with a printer.
OS - XP Pro
Printer - Canon BJC - 85
Normally when I print using this printer I get a pop up box telling me that I do not have a color cartridge installed and would I like to replace it or ignore it. I click ignore and it prints away.
However when I have Spark running and I print I get the pop up box but often it does not complete painting and even if it does then it hangs. I am unable to click on any of the buttons. When I exit Spark the pop up finishes loading and I can complete printing.
I have yet to try this with other printers which I will do in the morning.
I am trialing Spark along with Asterisk-IM with a view to rolling it out to 450 Computer Troubleshooter Franchises worldwide.
Apart from this little glitch I am very impressed and the trial is going very well.