The source virtual machine or physical server is missing a CD-ROM drive. When "auto-install tools" is selected, the destination VM mirrors the source hardware and lacks the necessary CD-ROM device for the ESXi host to mount the VMware Tools installation ISO, resulting in the mount failure.
Option A: Pre-Conversion Hardware Modification
Before initiating the conversion task, add a virtual CD-ROM drive to the source virtual machine.
Run the VMware vCenter Converter Standalone task with "auto-install tools" enabled. The destination VM will inherit the CD-ROM drive, allowing the automated installation to succeed.
Option B: Post-Conversion Manual Tools Installation If the conversion has already completed or the source machine cannot be modified:
In the vSphere Client, right-click the successfully converted virtual machine and select Edit Settings.
Select Add New Device and choose CD/DVD Drive.
Connect the drive to the Datastore ISO File or Client Device and click OK.
Power on the virtual machine.
Initiate a manual VMware Tools installation via the vSphere Client.