Oracle Database Discussions

I wondering if anyone else has run into this issue before as I am finding this strange. When I try to increase the shared_pool or sga I get a ORA-04033: Insufficient memory error. Basically I am using a SPFILE and I am changing the values dynamically and my scope=both. Now, when I use a CREATE PFILE from SPFILE and change the same values in the PFILE and then start the DB backup, it takes the changes perfectly and now the changes I wanted in the first are all there, but the only difference is I am using a PFILE instead of the SPFILE.

What happened here. Why would the PFILE allow me to make the changes I needed when Oracle is telling me ORA-04033: Insufficient memory with the SPFILE. Also, on the server, we have 4gb's of RAM and the server itself only has one Oracle DB running on it, so I was surprised as to why I could not allocate more memory for the DB. The settings were:

shared_pool = 152MB
SGA=350MB

I wanted to go to
shared_pool = 512MB
SGA=1024MB

SPFILE failed, and with the PFILE it worked.

Any thoughts?