I Googled the problem and found several "solutions" on the Crashplan website, one of which was to uninstall and reinstall Crashplan. I did that but it didn't solve the problem. Then I found this blog posting: http://www.levijackson.net/crashplan-pro-wont-start. Per the posting I changed -Xmx1024m to -Xmx512m in my C:\Program Files\CrashPlan\CrashPlanService.ini file. After making that change I found I was able to start in Crashplan service in the Windows control panel and Crashplan would run.
The next day when I started my computer Crashplan was nowhere to be found. In checking the CrashPlanService.ini file -Xmx512m had magically changed back to -Xmx1024m. I changed it back and was able to start the Crashplan service but every time I tried to run Crashplan -Xmx512m changed back to -Xmx1024m. The Crashplan service would stop and Crashplan wouldn't run.
I started looking through the error logs in C:\Documents and Settings\All Users\Application Data\CrashPlan\log and found a reference to my.service.xml located in C:\Documents and Settings\All Users\Application Data\CrashPlan\conf. Looking at that xml file I saw a line that said "
I have no idea why this suddenly became a problem or why this fixed it. BTW, I'm running Windows XP SP3.