When turning nintendo ds lite on it comes up with this message System date error! Please check NDS system date.

It is just an eol (End Of Live) in the software of your ds card.
Plug out your ds and remove your r4 card.
Plug on your ds and change the date to 2009.
Plug out your ds and insert your r4 cart.
Plug on your ds and you can play again.
Now there wil be new software on the internet who is an update on the old software, so if you want to renew your software ist there on the net.

Yesterday (31/April) I was doing a Google search on the R4i "System Date Error" problem and found the solution! Check out this blog post:

http://www.nds-gear.co.uk/blog/2010/05/nds-gear-solves-r4i-sdhc-system-date-error-problem/

Follow the instructions and use their software (for genuine R4i-SDHC cards only of course) and problem should be solved! Worked for me on a regular DSi console with the original R4i SDHC card, 4GB memory.

The date and time settings for your Nintendo DS migh have been changed, try to set the correct time and date. Here is an easy way to do that. Click here. Hope it helps.