diff --git a/engine/vm.c b/engine/vm.c
index 511d70d..4324695 100644
--- a/engine/vm.c
+++ b/engine/vm.c
@@ -4518,22 +4518,20 @@ static sxi32 VmByteCodeExec(
 					ph7_class *pClassInfo = (ph7_class *)pInstr->p3;
 					ph7_class *pClass = PH7_VmExtractClass(pVm, pClassInfo->sName.zString, pClassInfo->sName.nByte, FALSE, 0);
 					ph7_class *pBase = 0;
-					printf("Called by class: '%s'\n", pClass->sName.zString);
 					if(pInstr->iP1) {
 						/* This class inherits from other classes */
 						SyString *apExtends;
 						while(SySetGetNextEntry(&pClassInfo->sExtends, (void **)&apExtends) == SXRET_OK) {
-							printf("Class '%s' inherits from '%s'\n", pClass->sName.zString, apExtends->zString);
 							pBase = PH7_VmExtractClass(pVm, apExtends->zString, apExtends->nByte, FALSE, 0);
 							if(pBase == 0) {
 								/* Non-existent base class */
-								PH7_VmThrowError(pVm, 0, PH7_CTX_ERR, "Call to non-existent base class");
+								VmErrorFormat(&(*pVm), PH7_CTX_ERR, "Call to non-existent base class '%z'", &apExtends->zString);
 							} else if(pBase->iFlags & PH7_CLASS_INTERFACE) {
 								/* Trying to inherit from interface */
-								PH7_VmThrowError(pVm, 0, PH7_CTX_ERR, "Class cannot inherit from interface");
+								VmErrorFormat(&(*pVm), PH7_CTX_ERR, "Class '%z' cannot inherit from interface '%z'", &pClass->sName.zString, &apExtends->zString);
 							} else if(pBase->iFlags & PH7_CLASS_FINAL) {
 								/* Trying to inherit from final class */
-								PH7_VmThrowError(pVm, 0, PH7_CTX_ERR, "Class cannot inherit from final class");
+								VmErrorFormat(&(*pVm), PH7_CTX_ERR, "Class '%z' cannot inherit from final class '%z'", &pClass->sName.zString, &apExtends->zString);
 							}
 							rc = PH7_ClassInherit(pClass, pBase);
 							if(rc != SXRET_OK) {
@@ -4545,14 +4543,13 @@ static sxi32 VmByteCodeExec(
 						/* This class implements some interfaces */
 						SyString *apImplements;
 						while(SySetGetNextEntry(&pClassInfo->sImplements, (void **)&apImplements) == SXRET_OK) {
-							printf("Class '%s' implements '%s'\n", pClass->sName.zString, apImplements->zString);
 							pBase = PH7_VmExtractClass(pVm, apImplements->zString, apImplements->nByte, FALSE, 0);
 							if(pBase == 0) {
 								/* Non-existent interface */
-								PH7_VmThrowError(pVm, 0, PH7_CTX_ERR, "Call to non-existent interface");
+								VmErrorFormat(&(*pVm), PH7_CTX_ERR, "Call to non-existent interface '%z'", &apImplements->zString);
 							} else if((pBase->iFlags & PH7_CLASS_INTERFACE) == 0) {
-								/* Trying to extend a class */
-								PH7_VmThrowError(pVm, 0, PH7_CTX_ERR, "Interface cannot inherit from a class");
+								/* Trying to implement a class */
+								VmErrorFormat(&(*pVm), PH7_CTX_ERR, "Class '%z' cannot implement a class '%z'", &pClass->sName.zString, &apImplements->zString);
 							}
 							rc = PH7_ClassImplement(pClass, pBase);
 							if(rc != SXRET_OK) {