1. Make sure that the Retail SDK version is the same as Retail POS. Example: If your POS is version R3 CU8 you should also upgrade to CU8 your Retail SDK. (Some POS KBs may also have components for SDK)
2. Add references that are missing in your project. You can find it in retail POS folder. (figure 1) (C: \ Program Files (x86) \ Microsoft Dynamics AX \ 60 \ Retail POS )
Note: For customizations involving design, you may need to install the plug-in DevExpress. (but from what I understand of your problem, it would not be necessary at this time)
figure 1
3. Build your project (figure 2) and copy new Peripherals.dll ([...] \ Retail SDK [CU] \ POS Plug-ins \ POS \ bin \ Debug) to the extensions folder POS (C: \ Program Files (x86) \ Microsoft Dynamics AX \ 60 \ Retail POS \ Services \ Extensions)
figure 2
I Hope this Helps!
Regards,
Rodolfo Recalde