It may be helpful to briefly review the functionality of masks (both subnet and access list masks). In general the purpose of the mask is to indicate which bits in the address are significant and must match and which bits do not have to match.
In a subnet mask the binary 1 bits indicate significant must match bits. So in a subnet mask 255.255.255.0 says that the first three octets must match and we do not care what is in the fourth octet. A subnet mask of 0.0.0.255 would say that we do not care what is in the first three octets and do care what is in the fourth octet (and this maks is not logical for subnetting).
A mask for access lists is an inverse mask and in these masks the 0 bit indicates that it is significant and must match while a 1 bit means it does not need to match. So in an access list a mask of 0.0.0.255 means that the first three octets must match and the fourth octet does not matter. An access list mask of 255.255.255.0 would mean that we care only about the fourth octet. So the access list of:
access-list 1 permit 192.168.0.0 0.0.0.255
would mean that the first octet must be 192, the second octet must be 168, the third octet must be 0, and the fourth octet can be anything (which is what you want).
The access list of:
access-list 1 permit 192.168.0.0 255.255.255.0
would mean that the first octet can be anything, the second octet can be anything, the third octet can be anything, and the fourth octet must be 0.
There are two kinds of masks. You must remember which kind are used with subnets and which kind are used with access lists.
HTH
Rick
HTH
Rick
