I haven't had this problem before, but I made a large batch of buttercream and it came out gritty. Is there any way to remedy it?
It is 1/2 crisco, 1/2 butter.
I'm not sure about gritty...but it sounds like it may be your powdered sugar. Sometimes if powdered sugar is real old or just a nasty brand (I hate greatland PS) then it will have little nasty dried up balls in it that will be all in your buttercream. Make sure you use a fresh bag, also another tip is do not pour in all of your liquid and then your sugar on top of that. Cream butter and shortening, add some of the sugar, and then add your liquids intermittent as needed with more sugar. Thats another way to avoid making your own hardened sugar balls from the sugar absorbing up all the vanilla/milk and getting hard.
You might want to try sifting your powdered sugar & using 10x as well if you've done that before. The sifting will take out any lumps & sometimes I end up sifting out little bits of hard sugar that I never would have seen. If you've sifted & used 10x, then I'm interested in what happened as well. 
HTH
It must be because I put all the liquid in at first, then the PS. Thank you for your help. I sifted my PS, but you never know. What does 10X mean?
10X is powdered sugar. I had the same problem with gritty icing. I found a couple hints on here that really helped. The first is to slowly add the PS, one cup at a time, mixing in between. When all of the PS has been added, then continue mixing on low or medium for another 8 to 10 minutes. Since I started doing that, I rarely ever have gritty icing anymore. The other thing I found that helped is to use all butter instead of butter & Crisco.
One thing that I have learned, is to read the "ingredients" on the powdered sugar label. It SHOULD say "sugar, cornstarch". But some brands (like Walmart brand) use BEET sugar...stay away from the beet sugar, it's more gritty. After I learned of this, I stick to only C&H brand!
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