Hi Richard,
You've browsed one folder too much!
Before the DatabaseOptions folder, there should be a folder called 'Database'. That's where you need to create the 'String Value'.
If you're using a 64-bit machine, you need the string value to be in:
HKEY_LOCAL_MACHINE\SOFTWARE\Wow6432Node\SAP BusinessObjects\Suite XI 4.0\Crystal Reports\Database
If it's a 32-bit machine then the path would be:
HKEY_LOCAL_MACHINE\SOFTWARE\SAP BusinessObjects\Suite XI 4.0\Crystal Reports\Database
Also, the string value needs to be created by the name InvalidAliasCharList and it's value should be .:{}()@&$#^!*~|%\\\"
Hope this helps.
-Abhilash