NEC ND-6500A Incompatible Media Error Message

I have recently purchased and installed a NEC ND-6500A with 2.24 firmware in my laptop, in addition to the Toshiba SD-R6372 that was already there. Initially, the NEC 6500A refused to burn anything with "Cannot write media - Incompaible Format". I purchased some Verbatim 16 x plus and minus R disks and voila it liked the plus disks and started burning with no problems. However, it still refused to burn the minus disks. I have since bought some Taiyo Yuden and Sony minus R disks but am still having the same problem. I have tried the drive as both master and slave. I have also changed the firmware to 2.58 and 2.81 using Binflash v.1,17 but still no luck.. Have since changed back to the original 2.4 firmware.

Please, if anybody can shed any light as to why I can't burn -R disks I would be so greatful. Below is a sample error log from DVD Decrypter.

I 06:34:06 DVD Decrypter Version 3.5.4.0 started!
I 06:34:06 Microsoft Windows XP Professional (5.1, Build 2600 : Service Pack 1)
I 06:34:06 Initialising SPTI...
I 06:34:06 Searching for SCSI / ATAPI devices...
I 06:34:07 Found 2 DVD-ROMs and 2 DVD±RWs!
I 06:34:23 Operation Started!
I 06:34:23 Source File: C:\Documents and Settings\My Documents\My Videos\SWD.ISO
I 06:34:23 Source File Sectors: 2,285,856 (MODE1/2048)
I 06:34:23 Source File Size: 4,681,433,088 bytes
I 06:34:23 Source File Implementation Identifier: DVD Shrink
I 06:34:23 Destination Device: [1:0:0] _NEC DVD+-RW ND-6500A 2.24 (F:) (ATA)
I 06:34:23 Destination Media Type: DVD-R (Disc ID: TYG02) (Speeds: 2x, 4x, 6x, 8x)
I 06:34:23 Destination Media Sectors: 2,297,888
I 06:34:23 Write Mode: DVD
I 06:34:23 Write Type: SAO
I 06:34:23 Write Speed: 8x
I 06:34:23 Link Size: Auto
I 06:34:23 Test Mode: Yes
I 06:34:23 BURN-Proof: Enabled
E 06:34:50 Failed to Reserve Track! - Cannot Write Medium - Incompatible Format
E 06:34:54 Operation Failed! - Duration: 00:00:29
I 06:34:54 Average Write Rate: N/A - Maximum Write Rate: N/A

Many thanks.