It sounds like something in your environment has changed. Access Denied generally means that there is a permissions issue. Please start by going through the troubleshooting guide step by step to help pinpoint where the issue is.
It might be caused by your anti malware software blocking psexesvc.exe on the target computers. Try setting a custom name for this process under ‘Tools > Settings > Remote Execution > Use PsExec -r switch to specify remove service name’ You could use something like BatchPatchExeSvc.exe. This might be enough to bypass the anti malware app. If not then you could try whitelisting the exe files in the anti malware app.