Sorry about that - here's the log from one of the failed attempts at burning:
I 00:13:26 ImgBurn Version 2.5.5.0 started!
I 00:13:26 Microsoft Windows 7 Home Premium Edition (6.1, Build 7601 : Service Pack 1)
I 00:13:26 Total Physical Memory: 3,136,624 KB - Available: 1,690,664 KB
W 00:13:26 Duplex Secure's SPTD driver can have a detrimental effect on drive performance.
I 00:13:26 Initialising SPTI...
I 00:13:26 Searching for SCSI / ATAPI devices...
I 00:13:26 -> Drive 1 - Info: ATAPI iHAS422 8 4L18 (E:) (ATA)
I 00:13:26 -> Drive 2 - Info: ATAPI iHOS104 WL0D (F:) (RAID)
I 00:13:26 Found 1 DVD±RW/RAM and 1 BD-ROM!
I 00:13:31 Operation Started!
I 00:13:31 Device: [1:0:0] ATAPI iHAS422 8 4L18 (E:) (ATA)
I 00:13:31 Media Type: DVD+RW (Disc ID: SONY-S11-00) (Speeds: 4x)
I 00:13:31 Quick Erase: No
I 00:13:31 Format Properly: Yes
I 00:13:31 Format Size: Preferred
I 00:13:31 Erasing Disc...
I 00:28:46 Operation Successfully Completed! - Duration: 00:15:14
I 00:28:56 Operation Started!
I 00:28:57 Source File: C:\Users\Mark\Desktop\test\1000176118.MDS
I 00:28:57 Source File Sectors: 2,079,339 (MODE1/2048)
I 00:28:57 Source File Size: 4,258,486,272 bytes
I 00:28:57 Source File Volume Identifier: 1000176118
I 00:28:57 Source File Volume Set Identifier: 3d6580f2
I 00:28:57 Source File Implementation Identifier: Sonic Scenarist 3.1
I 00:28:57 Source File File System(s): ISO9660, UDF (1.02)
I 00:28:57 Destination Device: [1:0:0] ATAPI iHAS422 8 4L18 (E:) (ATA)
I 00:28:57 Destination Media Type: DVD+RW (Disc ID: SONY-S11-00) (Speeds: 4x)
I 00:28:57 Destination Media Sectors: 2,295,104
I 00:28:57 Write Mode: DVD
I 00:28:57 Write Type: DAO
I 00:28:57 Write Speed: 4x
I 00:28:57 Link Size: Auto
I 00:28:57 Lock Volume: Yes
I 00:28:57 Test Mode: No
I 00:28:57 OPC: No
I 00:28:57 BURN-Proof: Enabled
I 00:28:57 Write Speed Successfully Set! - Effective: 5,540 KB/s (4x)
I 00:28:57 Book Type Setting: DVD-ROM
I 00:28:57 Advanced Settings - Force HT: No, Online HT: No, OverSpeed: No, SmartBurn: Yes
I 00:28:57 Filling Buffer... (40 MB)
I 00:28:58 Writing LeadIn...
W 00:28:58 Failed to Write Sectors 416 - 447 - Reason: Logical Unit Communication Time-Out
W 00:28:58 Retrying (1 of 20)...
W 00:29:01 Retry Failed - Reason: Write Error
W 00:29:01 Retrying (2 of 20)...
I 00:29:01 Writing LeadIn...
I 00:29:01 Writing Session 1 of 1... (1 Track, LBA: 0 - 2079338)
I 00:29:01 Writing Track 1 of 1... (MODE1/2048, LBA: 0 - 2079338)
W 00:29:01 Failed to Write Sectors 1248 - 1279 - Reason: Logical Unit Communication Time-Out
W 00:29:01 Retrying (1 of 20)...
W 00:29:03 Retry Failed - Reason: Write Error
W 00:29:03 Retrying (2 of 20)...
I 00:29:03 Writing Sectors...
W 00:29:05 Failed to Write Sectors 5952 - 5983 - Reason: Logical Unit Communication Time-Out
W 00:29:05 Retrying (1 of 20)...
I 00:29:05 Writing Sectors...
W 00:29:08 Failed to Write Sectors 13600 - 13631 - Reason: Logical Unit Communication Time-Out
W 00:29:08 Retrying (1 of 20)...
W 00:29:09 Retry Failed - Reason: Logical Unit Communication Time-Out
W 00:29:09 Retrying (2 of 20)...
I 00:29:09 Abort Request Acknowledged
I 00:29:10 Writing Sectors...
I 00:29:11 Synchronising Cache...
W 00:29:14 User opted to skip the 'Close Track/Session/Disc' functions.
E 00:29:14 Failed to Write Image!
I 00:29:14 Exporting Graph Data...
I 00:29:14 Graph Data File: C:\Users\Mark\AppData\Roaming\ImgBurn\Graph Data Files\ATAPI_iHAS422_8_4L18_SUNDAY-JUNE-05-2011_12-28_AM_SONY-S11-00_4x.ibg
I 00:29:14 Export Successfully Completed!
E 00:29:14 Operation Aborted! - Duration: 00:00:17
I 00:29:14 Average Write Rate: 3,029 KB/s (2.2x) - Maximum Write Rate: 5,206 KB/s (3.8x)
I 00:29:15 Close Request Acknowledged
I 00:29:15 Closing Down...
I 00:29:20 Shutting down SPTI...
I 00:29:20 ImgBurn closed!
I wasn't aware that .mds files weren't plain text. So I guess there's nothing wrong with the .mds files then? So I wonder what was causing the problem? Hopefully the log can tell you something.