When I tried to create an account in v3 I'm getting an error:
Unhandled exception: Licensing error in /usr/local/centovacast/system/class_RPCDaemonClient.php:1028

#0 /usr/local/centovacast/system/class_RPCDaemonClient.php(1028): RPCDaemonClient::parse_response()
#1 /usr/local/centovacast/system/class_RPCDaemonClient.php(1042): RPCDaemonClient->parse_response()
#2 /usr/local/centovacast/system/class_RPCDaemonClient.php(1091): RPCDaemonClient->get_response()
#3 /usr/local/centovacast/system/class_RPCDaemonClient.php(950): RPCDaemonClient->send('fcfbf52606757d3...')
#4 /usr/local/centovacast/system/class_RPCDaemonClient.php(1069): RPCDaemonClient->authenticate()
#5 /usr/local/centovacast/system/class_RPCDaemonClient.php(1010): RPCDaemonClient->send()
#6 /usr/local/centovacast/system/class_RPCDaemonClient.php(800): RPCDaemonClient->command()
#7 /usr/local/centovacast/system/class_SystemControl.php(1164): RPCDaemonClient->info()
#8 /usr/local/centovacast/system/class_SystemControl.php(322): SystemControl->api_provision()
#9 /usr/local/centovacast/web/class_AccountEditor.php(896): SystemControl->__call('provision', Array)
#10 /usr/local/centovacast/web/class_AccountEditor.php(315): AccountEditor->provision_account()
#11 /usr/local/centovacast/web/reseller/modules/class_Module_accounts_base.php(65): AccountEditor->create()
#12 /usr/local/centovacast/web/admin/modules/class_Module_accounts.php(48): Module_accounts_base->create_account()
#13 /usr/local/centovacast/web/class_WebApplication.php(224): Module_accounts->execute()
#14 /usr/local/centovacast/web/admin/class_AdminApplication.php(64): WebApplication->execute()
#15 /usr/local/centovacast/web/admin/index.php(49): AdminApplication->execute()
#16 {main}

Please search before posting; this has already been addressed many times.  That means you have a licensing error of some sort, and this message is intentionally vague to avoid disclosing any potentially embarrassing information to your clients (eg: that you are behind on payments or somesuch).  Check your logs or restart Centova Cast to find out the exact nature of the error.