Try this

src/primitives/block.h

@@ -30,6 +30,15 @@
 
 extern int32_t ASSETCHAINS_LWMAPOS;
 
+class CPOSNonce : public uint256
+{
+public:
+    CPOSNonce() : uint256() { }
+    CPOSNonce(const base_blob<256> &b) : uint256(b) { }
+    CPOSNonce(const std::vector<unsigned char> &vch) : uint256(vch) { }
+};
+
+
 /** Nodes collect new transactions into a block, hash them into a hash tree,
  * and scan through nonce values to make the block's hash satisfy proof-of-work
  * requirements.  When they solve the proof-of-work, they broadcast the block
@@ -52,8 +61,8 @@ public:
     uint256 hashFinalSaplingRoot;
     uint32_t nTime;
     uint32_t nBits;
-    //CPOSNonce nNonce;
-	uint256 nNonce;
+    CPOSNonce nNonce;
+	//uint256 nNonce;
 
     std::vector<unsigned char> nSolution;