Is the plugins order important

Yes sir/madam, the plugins order is very important for AceSEF.

To be more specific, the System type plugins order does affect AceSEF's functionality. So this is the order that your System plugins should be ordered:
  • Other plugins
  • System - AceSEF
  • Cache plugins

For more details check the following article:
http://www.nonumber.nl/news/blog/463-plugin-order-is-important