###GolfScript, 28 26 characters###

:I,,{)I/();\+.-1%=}?-2]0=)

Thanks to Peter for shortening by 2 characters. Try the test cases online:

> "RACECAR" 
4
> "RAACECAR" 
2
> "RAAACECAR" 
-1
> "ABCC1BA" 
5
> "AAAAAA" 
1
> "ABCDE" 
-1
> "" 
-1
> "A" 
1

GolfScript, 28 26 characters

:I,,{)I/();\+.-1%=}?-2]0=)

Thanks to Peter for shortening by 2 characters. Try the test cases online:

> "RACECAR" 
4
> "RAACECAR" 
2
> "RAAACECAR" 
-1
> "ABCC1BA" 
5
> "AAAAAA" 
1
> "ABCDE" 
-1
> "" 
-1
> "A" 
1

###GolfScript, 28 characters###

:I,,{)I/();\+.-1%=}?-2]$-1=)

Try the test cases online:

> "RACECAR" 
4
> "RAACECAR" 
2
> "RAAACECAR" 
-1
> "ABCC1BA" 
5
> "AAAAAA" 
1
> "ABCDE" 
-1
> "" 
-1
> "A" 
1

###GolfScript, 28 26 characters###

:I,,{)I/();\+.-1%=}?-2]0=)

Thanks to Peter for shortening by 2 characters. Try the test cases online:

> "RACECAR" 
4
> "RAACECAR" 
2
> "RAAACECAR" 
-1
> "ABCC1BA" 
5
> "AAAAAA" 
1
> "ABCDE" 
-1
> "" 
-1
> "A" 
1