It is not at all required to uninstall SP03 if you want to upgrade it to higher version. I was having some issue on my system so i had to uninstall and install latest SP. Please don't confuse with that.
Compatible version of SAP Mobile Platform Server is not installed on the system. Cannot upgrade to SAP Mobile Platform Server 3.0 SP04 PL1.
Coming to your query, if you are trying to execute SP04PL01 over SP03, it will not allow to do so because SP04PL01 requires SP04 to be install OR SP03 to be upgraded to SP04 first. So please upgrade SP03 to SP04 first and then apply PL01 over it.
Hope you get it now.
Regards,
JK