Question : Which Pervasive do I need??

Here is my predicament. I'm a Microsoft guy and know SQL, but on Pervasive I don't have a clue on how it's licensed.
I'm helping a small client who uses Pervasive 8.0 currently on their PC's and laptops and a small busines server. They are using the Workgroup Edition of Pervasive.  The software that uses it is on each PC & laptop along with pervasive and synch's with the server when they return to the office. They just bought two new laptops with Windows 7. They guy's who sells the software they use said they had to upgrade the Pervasive to v10 on Windows 7. He wouldn't or couldn't give clear direction on what to buy. I found a company and quizzed them on the Workgroup Edition with 5 users would work with their scenario and they said it sounded right.
I installed it on one of the laptops all is good. When I installed it on the second laptop it's telling me the serial number has already been used. I'm stuck on stupid here and looking for direction. Did I buy the right thing or installing things wrong??

Answer : Which Pervasive do I need??

You have to buy licenses for each computer.  THe 5 user license is not licensed for 5 computers but allows 5 users to connect to the engine.   You'll need a 5 user license on each machine unless you can get a single user license (I'm not sure what's available from a license key standpoint).  
Which company did you talk to?  I would suggest contacting Pervasive directly (1-800-287-4383 in the US).  They should be able to straighten you out.  

One more item of note, the PSQL v10 engine on the laptop may have problems connecting to the server if it's running PSQL v8.  Ideally you would upgrade all clients and the server to PSQL V10.