Tidy skips large files?

Hello?
I have a question here!!
Tidy skips large files?
I use the Tidy DLL in VB , TidyMemToMem(sourceString)
And when I used a tidy, there is a good job
But when I using a tidy large pages (eg. www.nba.com
<http://www.nba.com/> )  it return  null string 
Is there a size limit for the string size?
If yes, how can I solve the problem?
 
Regards.
Won Ju.