Thank you, acer. I restarted the whole computer system and now it seems that no such memory restriction problem any more. Thank you for your advice!

The operating system is Windows Server 2003 Stardard Edition. Thank you!

Dear Alec and Acer, thank you very much for you comments and detail explanations. Now there is still one more question: Since there is 4G physical memory on my machine, why Maple terminates when consuming only roughly 500M memory, which seems to be due to memory limitations.

Error, (in Matrix) not enough memory to allocate rtable

Error, (in Matrix) Maple was unable to allocate enough memory to complete this computation.  Please see ?alloc

But "kernelopts(datalimit)" shows that there is no limitation on the memory consuming. How can I use more memory, say 1.5G, so that I can handle even larger size matrices. Thank you very much!!