Hi Elia,
My thoughts are: as you have already created a project after selecting target runtime as "sap mobile platform 3.0 SP04" in kelper but you are deploying to SP05.
You may try below steps:
1. First update plugins as Midhun suggested.
2 . right click over project (in eclipse) and check if you see any option to migrate existing proj to SP05
(You may also check if you see any option to SP05 under "target runtime" while creating a new proj)
3 . deploy the proj (you may try with remaining proj name and changing version)
Regards,
JK
ps: I haven't tried it yet, will let you know soon.