Applying catalog rules gives a blank screen or exhausts memory or exhausts maximum execution time

Applying rules is a heavy process so it's likely you're not doing anything wrong. If you're seeing a white screen instead of a memory or max time exhausted fatal error, it's probably because you have error reporting turned off.

However, MageRewards only add about 5 seconds and a few KB to what Magento’s catalog rule application process already uses. The general rule is: If you can’t apply regular (non-MageRewards) Magento Catalog Promotion Rules, then you can’t apply MageRewards catalog points rules. So, try to create a Magento Promotion rule and apply rules to see if you get the same issue. Here are approximate requirements for Magento’s catalog rule application process:

• It takes an average of 0.5 seconds per product to apply rules (approx 600 simple products = 5 minutes)
• It takes about 0.5mb per product to apply rules (approx 600 simple products = 5 mb)

To resolve either:

• Edit the .htacess and change the max execution time or memory limit to something more
• Ask your server administrator or web host to increase the max execution time or memory limit to something more
• Reduce the number of enabled products in your store (although that's unlikely to be a good solution)
• Use Shopping Cart points rules instead.