*EDIT*
I recently had the "data.cab" Error. The problem with this Error is that no matter how many times you do a fresh reinstall of MS, the computer always sees the download as corrupt. Some people have had luck using the RAR installation files and I was in the process of downloading them too, when I finally tried this:
I loaded MS from an old iTCG CD. I bought the Cards around v.47 and installed it a few days after v.52. I made sure Firewalls and Virus Protection was off while MS uploaded from the CD and while MS downloaded the v.52 Patch. I also made sure no other programs were running except what was in the "Background".
Also, before I could even get the .msi program (MicroSoft Install Shield file) to extract properly, I had to permanently delete a very strange MapleStory program in the Add/Remove Programs. I say wierd because not only did I "Remove" MS properly through Add/Remove, but I also deleted as many traces of it as I could find elsewhere. I did some digging around on google and found I had to install "Microsoft Install Shield Clean Up" utility program. I ran this and selected the wierd MapleStory program in Add/Remove and finally got rid of it to where the .msi thing could see that there was NOT an old version of MapleStory on my computer.
*~fin~ EDIT*

(I'll post this in a couple Forum Sections then delete when neccessary):
try this first:
http://www.basilmarket.com/forum/335747/0//Patch_Problem_Solutions__Check_First.html

Now... did you try the "Manual Patcher" at Nexon.net, up top, under "Downloads"/"-Games/Patches"; scroll down a bit and pick the big RED Manual Patch button - ...RUN IT (BUT make sure your FIREWALL IS TURNED OFF & that you have NO other programs running)
To turn your firewall off do this (for those who may not know):
Clicking Start, then goto settings/control panel/Security Center/Windows Firewall - TURN IT OFF WHILE DOWNLOADING THE PATCH OR THE ORIGINAL "CLIENT" (the client is the whole "Fresh" Re-Install)

To do a "Fresh" Re-Install you need to UnInstall MapleStory as it exists on your computer to begin with. Goto "Start/Settings/Control Panel/Add Or Remove Programs"!
Now Un-Install MapleStory... then,also, go to "Program Files" (or wherever MS is stored on your comp.) and delete the Nexon Folder!
Now REBOOT!
Come back to Nexon.net and goto GAME DOWNLOAD on the left. Make sure Firewall(s) are still turned off and Install the whole MS Program again...

Other Suggestions:
1. Run Anti-Virus software (i hope you have it - AVG is free and very worthy; google it - Grisoft provides it)

2 Run Anti-Spyware (Ad-Aware and Spybot Search & Destroy are good)

3. "Free up space on your hard disk" in the 'Control Panel' under "Performance and Maintenance" in the 'Category View' of Windows XP) - sry that's all I run ...is Winows XP Home Version...

4. Again, in the 'Category View' of the Control Panel, DEFRAG YOUR COMPUTER under 'Performance and Maintenance! This greatly increases the speed of your computer and then some.

REBOOT (restart) your computer - Possibly even after each of these steps (..ummm also it is recommended that you run each of these steps in "Safe Mode", but let's not worry about that right now)

Confused yet... sry, just trying to help is all
.
If all else fails try the Sticky Thread at nexon.net Forums called "Technical Issues - Read Me First" or the "General Problems" faq. This is A GREAT RESOURCE FOR ERROR CODES AND SUCH... http://forum.nexon.net/MapleStory/forums/62/ShowForum.aspx

GOOD LUCK AND HAPPY MAPLING
Feel free to ask questions (I know some of this is probably confusing, but I'm just trying to help 0.o) - BTW I'm playing MS right now

ALSO, Our good friend Basil market has good Tech help section (regarding black-screen and such):
http://www.basilmarket.com/show/forum/15

D/C'ing:
(found this at Hidden-Street)
1. Go to Your Nexon Folder
2. Right click Maplestory.exe (in the folder)
3. Click Properties
4. Click Compatibility
5. Click Run this mode in compatibilty mode for
6. Click Windows98/ME
7. GO PLAY! What are you looking at?
(But the thing is.. You have to do this everytime you start playing)