The community answers a tremendous amount of discussions and the MVPs are all volunteers with other jobs. These errors are very difficult to address remotely since there could be a myriad of issues (firewall, GPO, UAC, sharing, creds, etc...)
Are you trying to push an Advanced Agent, SelF EXE, etc...? What credentials are you using for the Scheduler service? Can you ping the device from the core (short/FQN)? Is port 12174 open? Any logs on the client? What OS is the client? Firewall/Antivirus issue? It could be a hundred items.... Best thing to do since it was working before is to open a case with LANDesk.