Crystal Report Viewer Error: "CRAXDRT Error Occured on Server. 507 : An Exception Occ

We have recently setup Window Server 2003 SP2 (IIS V6.0) with Crystal Report 8.5 installed. All things working well for report viewer in internet browser, but only the problem is when user trying to export report to a file (CR/word/rich text/etc format) will hit the error:

CRAXDRT Error Occurred on Server. 507 : An exception occurred

Only option is click "OK" to continue... Well, so we just click "OK" and try again... Note that, for second tried onward will hit another error:

CRAXDRT Error Occurred on Server. 70 : Permission denied

It was annoying us as export crystal report to a file is the major part for our daily operation. We have search over the intranet and there are so many similar cases but without a clear direction where this error was hitted.

In addition, I have done some permission setting between my website in IIS and CR Viewer, i.e. shared viewer to the website, set permission of viewer to allow access of anonymous intranet user... unfortunately still can't work...

Look forward to experienced to share the solution/opinion. Thanks!

Try setting "write" permissions to C drive root directory for NT account that runs IIS.
Permissions needs to be set only to C-root an not need to be propagated to any underlying directories.
With time I can investigate details of what exactly Crystall needs to write on C drive root directory

Thanks jggts!

Still can't work at my end...
I have set the permission of root (C, D) to allow Everyone to do Everything, restart server, restart IIS etc...

But I wonder why the "Read-Only" check boxes of all folders in C: and D: always in Gray color mode (maybe indicate it is partial Read-Only?) no matter I have unchecked it for hundred times...

nearly desperate... still can work even already open permission to EVERYONE for root directory... :(

Btw, I'm using CR8.5 in this case...