Unable to manually manage music on more than one computer

Recently i had some problems with my iphone so i decided to delete all the music and start over again, i enabled the manually manage music in my work pc and then drag and drop my songs into the iphone library, all happened fine, then when i got home i connected my iphone to my laptop and i noticed that the manually manage music are unchecked and my iphone´s library dont allow me to add or delete songs! do anyone knows what´s the problem? i have the same itunes version wich is the latest on both computers, this is the 11.1.3.8

I will appreciate any help!