Page Access Permissions for Users

The following table lists the permissions required of users for Approval pages:

Apex Page	Enabled
AdhocProcessRuntime	TRUE
AgreementApprovalSummary	TRUE
AgreementApprovalSummarySf1	TRUE
AgreementLineItemApprovalSummary	TRUE
AgreementTermExAdd	TRUE
AgreementTermExApprovalSummary	TRUE
AgreementTermExApprovals	TRUE
AgreementTermExCancel	TRUE
AgreementTermExEdit	TRUE
AgreementTermExHistory	TRUE
AgreementTermExPreview	TRUE
AgreementTermExSubmit	TRUE
ApprovalAction	TRUE
ApprovalActionSf1	TRUE
ApprovalContextCancel	TRUE
ApprovalContextPreview	TRUE
ApprovalContextSubmit	TRUE
ApprovalMatrixGenerate	TRUE
ApprovalMatrixView	TRUE
ApprovalProcessDefn	TRUE
ApprovalProcessDefnList	TRUE
ApprovalProcessFinalAction	TRUE
ApprovalProcessInitialAction	TRUE
ApprovalProcessSelectEmailTemplate	TRUE
ApprovalProcessStep	TRUE
ApprovalProcessStepView	TRUE
ApprovalRequestAttachment	TRUE
ApprovalRequestEscalate	TRUE
ApprovalRequestReassign2	TRUE
ApprovalRequestReassign2Sf1	TRUE
ApprovalRequestsList	TRUE
ApprovalRequestsListSf1	TRUE
ApprovalRule	TRUE
ApprovalRuleCriteriaEdit	TRUE
ApprovalRuleDimension	TRUE
ApprovalRuleEntry	TRUE
ApprovalSummaryLaunch	TRUE
ApprovalSummaryLaunchAddCommentSf1	TRUE
ApprovalSummaryLaunchApproveRejectSf1	TRUE
ApprovalSummaryLaunchReassignSf1	TRUE
ApprovalsJSLibInclude	TRUE
BackupApprover	TRUE
BackupApproverAction	TRUE
BackupUserSearch	TRUE
DelegateApprovers	TRUE
FormulaField	TRUE
MatrixUserSearch	TRUE
MyApprovals	TRUE
MyApprovalsLaunch	TRUE
MyApprovalsSf1	TRUE
NextLevelApprover	TRUE
OpportunityApprovalSummary	TRUE
OpportunityPartnersList	TRUE
OpportunityProductsList	TRUE
PreviewSubmitApprovals	TRUE
QueueSearch	TRUE
ReassignUserSearch	TRUE
ReassignUserSearchMyApprovals	TRUE
SObjectApprovals2Submit	TRUE
SObjectApprovals2SubmitSf1	TRUE
SearchFilter	TRUE
SearchFilterDetail	TRUE
TermExApproval	TRUE
TermExApprovalClone	TRUE

For information on setting page access permissions, refer to this Salesforce article.