First,just use ePSXe 1.4.0,you won't have the memory card problem anymore.
Then,null's SPU only supports savestates in version 1.35(you'd better use Iori's SPU or the internal one since null's SPU is discontinued).
For the savestate loading problem,load your savestate from disc one,and then change disc.
Also,update your GPU,Pete released his version 1.51 a while back(I bet you've been away a llllooooonnnnggggg time
).
Then,null's SPU only supports savestates in version 1.35(you'd better use Iori's SPU or the internal one since null's SPU is discontinued).
For the savestate loading problem,load your savestate from disc one,and then change disc.
Also,update your GPU,Pete released his version 1.51 a while back(I bet you've been away a llllooooonnnnggggg time