OTA Update fails to install on HTC one M9. Help!

I recently bought an Unlocked HTC one M9 from eBay. It was on Android 5.0.2 (1.32.617.6) and I received an update notification for 1.32.617.30. When I clicked to install it, it fails saying error in cache with error 7. I think since it's a used phone the device software has been tampered before therefore the OTA update fails. I don't know the device history.This is what I found in bootloader mode.
Software status: Official
S-OFF
Bootloader:Locked
It is super CID (11111111)
And it has stock recovery.

I have tried flashing 1.32.617.6 stock ROM from stock recovery after I found it on XDA. It also failed saying signature verification failed. I searched this forum and found that someone had the same issue and they had to flash 1.32.617.6 using a SD card formatted to FAT32. I don't have a SD card so I couldn't try it.

I also tried HTC's latest RUU. EXE for Unlocked/Developer edition but it doesn't run well. It starts and shuts down after it asks me to agree to terms and conditions. I have latest HTC sync manager and it recognizes my phone. I will be trying this again on some other computer.

I really want to update my device to the latest version of OS. Please help me! I don't know what else to try.