Error mounting InstallESD Image

I'm trying to install Catalina on my late 2008 MacBook running on El Capitan using a patcher

I've gotten to the point where I create the bootable installer on an external drive. When I start the creation, I get about half way through before receiving this error message:

Error Mounting InstallESD Image

An error occurred while mounting the InstallESD image. Verify that InstallESD.dmg is not mounted using Disk Utility, then try again.

Here is the log:

Mounting BaseSystem.dmg...

/dev/disk3          	GUID_partition_scheme          	
/dev/disk3s1        	Apple_HFS                      	/private/tmp/basesystem


Patching BaseSystem.dmg...

"disk3" unmounted.
"disk3" ejected.
Preparing imaging engine…
Reading Protective Master Boot Record (MBR : 0)…
   (CRC32 $05BD9B8F: Protective Master Boot Record (MBR : 0))
Reading GPT Header (Primary GPT Header : 1)…
   (CRC32 $0B9401A9: GPT Header (Primary GPT Header : 1))
Reading GPT Partition Data (Primary GPT Table : 2)…
   (CRC32 $DFDDEEE9: GPT Partition Data (Primary GPT Table : 2))
Reading  (Apple_Free : 3)…
   (CRC32 $00000000:  (Apple_Free : 3))
Reading disk image (Apple_HFS : 4)…
   (CRC32 $BB653CB5: disk image (Apple_HFS : 4))
Reading  (Apple_Free : 5)…
   (CRC32 $00000000:  (Apple_Free : 5))
Reading GPT Partition Data (Backup GPT Table : 6)…
   (CRC32 $DFDDEEE9: GPT Partition Data (Backup GPT Table : 6))
Reading GPT Header (Backup GPT Header : 7)…
   (CRC32 $0A9BF70B: GPT Header (Backup GPT Header : 7))
Adding resources…
Elapsed Time: 40.625s
File size: 697873585 bytes, Checksum: CRC32 $C02663E9
Sectors processed: 4189376, 3563452 compressed
Speed: 42.8Mbytes/sec
Savings: 67.5%
created: /private/tmp/BaseSystem.dmg


Restoring BaseSystem.dmg...

	Validating target...done
	Validating source...done
	Retrieving scan information...done
	Validating sizes...done
	Restoring  ....10....20....30....40....50....60....70....80....90....100
	Remounting target volume...done
Volume on disk2s1 renamed to Catinstall


Copying SharedSupport to Volume...



Copying Patched BaseSystem.dmg...



Mounting InstallESD.dmg...

hdiutil: attach failed - no mountable file systems

Anyone know how I can fix this?