PDSC: Sequence Execution failed error


I am trying to flash code onto the STM32F303 microcontroller on Keil uVision5 MDK-ARM v5.31 using the ULINK2 JTAG debugger. I have the latest packs for the STM32xx_DFP (v2.1.0). Now, whenever I try entering Debug Mode on Keil, I get a "ULINK2/ME - Cortex-M Error" popup message saying: "PDSC: Sequence Execution failed".

Below is the description in the 'Build Output' section:


Cannot access Memory (@ 0xe00fffe4, Read, Acc Size: 4 Byte)

File                    : C:\Users\<username>\AppData\Local\Arm\Packs\Keil\STM32F3xx_DFP\2.1.0\Keil.STM32F3xx_DFP.pdsc

Sequence          : DebugDeviceUnlock -> CheckID

Context              : Item #0: <block>::Line 11

Expression         : "\<username>\AppData\Local\Arm\Packs\Keil\STM32F3xx_DFP\2.1.0\Keil.STM32F3xx_DFP.pdsc"

E310                  : Debug access failed - cannot read address 0xE00FFFE4 (accsize, '4', AP '0x00000000')

Cannot access Memory (@ 0x00000000, Write, Acc Size: 4 Byte)

Error: Flash Download failed - Target DLL has been cancelled


My Keil uVision software works fine with the STM32F303 series until a week ago. I am certain my JTAG debugger is not the issue because I am able to run Debug Mode using the JTAG debugger on a custom PCB with an STM32F410 chip. I also do not have issues when uploading code to the STM32F303RE Nucleo board through ST-Link (so I don't think the issue is with the STM32F3xx_DFP pack). Furthermore, this issue also occurs on the STM32F303C8 and STM32F303K8 when connected through the ULINK2 JTAG debugger. 

I have tried deleting the dbgconf file as suggested in this page: http://www.keil.com/support/docs/4057.htm. I also tried fully uninstalling Keil uVision5 from my laptop (running Windows 10 64-bit) and deleting the registries in Registry Editor along with Keil folders/files under <users>/AppData/Local/Arm and C:/Keil_v5, and reinstalling everything and the error still persists.

Are there any workarounds to this error? Why did the error appear even though Keil was behaving normally previously? Any help would be greatly appreciated. 

Thank you!

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