I have had a major issue (CRASH ON STARTUP) with Neverwinter Nights Diamond since I purchased and downloaded it from GOG several days ago. The crash was consistent, and the error message was always the same:

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Error Signature
AppName: nwmain.exe AppVer: 1.6.9.0
ModName: ntdll.dll ModVer: 5.1.2600.6055
Offset: (this changes every time)
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I worked on this problem for 36 hours straight (no sleep), and tried everything I could think of, and everything I could find on various forums to solve this issue. Steps taken: CLEAN re-install (i.e. UnInstall, Clean orphan entries in the registry (I use CCleaner from Piniform), Sometimes De-fragging the partition, Re-boot, Re-Download and Install the program). I made my Windows Firewall and Trend-Micro anti-virus 'friendly' to */Gog.com/* and re-downloaded. I tried several 'fixes' suggested by the GOG tech support team, even doing things that were done to the computer long ago. The results were always the same - CRASH ON STARTUP.

Then I went to this website, and the 'fix' turned out to be amazingly simple:

From: pcsupport.about.com/od/fixtheproblem/a/ntdlldll.htm

Applies To:

Ntdll.dll error messages can apply to nearly any Windows based software program, driver, or plugin on any of Microsoft's operating systems from Windows NT up through Windows 8, Windows 7, Windows Vista, and Windows XP.

How To Fix Ntdll.dll Errors

1. Restart your computer. The ntdll.dll error you're receiving could be due to a one-time, temporary issue and a simple reboot may resolve the problem completely.

2. Reinstall the program if the ntdll.dll error only displays when you use a specific program.

Steps 3 to 7 all have to do with Windows XP (or newer) or Internet Explorer (or Chrome). Since Neverwinter Nights was the only program I was having this problem with, I skipped all of these steps.

8. Update drivers for any hardware in your computer where updated drivers are available. Outdated drivers sometimes cause ntdll.dll errors.

NOTE: This seemed unlikely since other graphics intensive games (like Dungeon Keeper 2 and Silent Hunter IV) weren't having this problem, but at this point, what did I have to lose?
CONTROL PANEL\SYSTEM\HARDWARE tab\DEVICE MANAGER button\expand DISPLAY ADAPTERS\select ATI RADEON HD 2600 PRO\PROPERTIES button\DRIVER tab\UPDATE DRIVER button\select 'Install Software Automatically'. Windows did a search, then installed 'something'. Re-booted the Computer.

After the computer started up, I selected 'Neverwinter Nights Diamond' from the desktop icon, and VOILA!! NWN started up with no hesitation - Opening credits, music, intro movie and Main Menu. All selections after that worked properly, and I was able to select a Campaign, or Other Module (including ALL the Premium modules sent by GOG, as well as the Premium modules I had purchased from BioWare years ago. HAPPY, HAPPY, JOY, JOY!!

Upon further inspection, I found something really strange. Windows had actually 'rolled back' my driver to a previous edition.
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Display Devices
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Card name: ATI Radeon HD 2600 PRO
Manufacturer: Advanced Micro Devices, Inc.
Chip type: AMD Radeon Graphics Processor (0x9589)
DAC type: Internal DAC(400MHz)
Device Key: Enum\PCI\VEN_1002&DEV_9589&SUBSYS_33301545&REV_00
Display Memory: 512.0 MB
Current Mode: 1366 x 768 (32 bit) (60Hz)
Monitor: DELL E1910H
Monitor Max Res: 1366,768
Driver Name: ati2dvag.dll
Driver Version: 6.14.0010.7267 (English)
DDI Version: 9 (or higher)
Driver Attributes: Final Retail
Driver Date/Size: 7/3/2012 21:37:10, 306176 bytes

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Display Devices (Changes)
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** Current Mode: 1280 x 768 (32 bit) (60Hz)
** Monitor: Plug and Play Monitor
** Monitor Max Res: 1600,1200
Driver Name: ati2dvag.dll
** Driver Version: 6.14.0010.7179 (English)
DDI Version: 9 (or higher)
Driver Attributes: Final Retail
** Driver Date/Size: 4/5/2011 19:01:20, 302080 bytes

Quite bizarre NWN works with an earlier driver edition, but the other programs (mentioned above) still work too, so I'm not going to beef.

ISSUE SOLVED (for me)

If your ntdll.dll problem is more consistent and faulting with other programs, there are other steps to try at the above website.

This is Proteus signing off, and wishing you MANY GOOD LUCKS!