I'm trying to upgrade my son's ageing IBM PC by adding some memory. It is a 300PL with PIII processor. Motherboard is 6565EBG and it has two 128Mb SDRAM memory sticks. I've tried to add 512Mb but get 2 messages at POST. 206 Memory failed configuration and 164 Memory size error. I've tried various other combinations and it seems that it won't accept double sided memory sticks. Is there a solution?