RewriteRule Error: Bad flag delimiters

Turns out it was because of the space before N in the flag declaration [L,R=301, NC]. I changed it to [L,R=301,NC] and now it works a treat.

Check at the link below, and it will give you the line with error, which will be straight forward to fix

http://www.htaccesscheck.com/index.html

In your case it will clearly specify the bad flags in the below line, which can be corrected in their editor and check there itself.

RewriteRule ^dev/(.*)$ http://dev.example.com/$1 [L,R=301, NC]

to

RewriteRule ^dev/(.*)$ http://dev.example.com/$1 [L,R=301,NC]