Here are the non-obvious steps required to create a directory such that your ASP IUSR_* process can write to it:
1. Create a virtual directory using the IIS Management Console. Make sure to give it write permission:
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2. In Windows Explorer, select Tools –> Folder Options and click on the "View" tab. Scroll to the bottom and uncheck the "Use simple file sharing" checkbox. Click the Apply button.
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3. Browse to the directory in Windows Explorer, right-click on it, and select Properties. Select the "Security" tab.
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4. Click the "Add User" button and type "IUSR_****". Then click on the "Check Names" button, then click OK.
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5. Give IUSR_**** full control of the folder, click Apply:
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That’s it. Also, if you still have trouble with directory permissions from ASP, try granting the "browse" privilege (in IIS) to see if that fixes it.