Help? System Overload Message., Over Load Errors in Logic Options

[prid]

Hi,

I am having serious problems at the moment with the "System Overload error" message when working in Logic Pro.
Basically the CPU is overloading everytime i press my play button.
I am using a couple of hungy plug ins, but not that many?!? I have used this many before and it didn't happen. I have a g4 power book.with 867mhz.

Its not the Audio overloading because I have many of the tracks frozen and can check with the system performance bar.

Can anyone recommend a solution, other than not using as many plugs in. (iam using a couple of logic synths, then some logic effects) I have already grouped some plug-ins onto busses to reduce the power used.

Any suggestions, other than upping my ram?
Would a seperate hardrive help?

Thanks