1) Open Notepad as Administrator
2) Open this file
3) Edit the variable -Xmx512M
A recommendable amount is 1024M.
4) If you can still access the CrashPlan Desktop UI, open it. Double click the logo in the top right. This will open a CrashPlan service terminal; type restart, press enter.
Your CrashPlan software should no longer crash due to memory problems. If it does, then change that value to something higher.