diff --git a/VERSIONS.md b/VERSIONS.md
index 5c15ded..36ae2c4 100644
--- a/VERSIONS.md
+++ b/VERSIONS.md
@@ -1,4 +1,7 @@
 # <a id='history'>版本歷史</a>
+* PWA 9.0.1, Electron app 20.0.1:
+  * [修正] Electron app 啟動時偶爾讀取離線 DB 失敗。
+
 * PWA 9.0.0, Electron app 20.0.0:
   * [變更] 用 JS 改寫讀取檔案系統離線 DB 程式碼。
   * [新增] 樹狀目錄新增知名經典目錄。
diff --git a/buildElectron/io.github.mrmyhuang.cbetar2.metainfo.xml b/buildElectron/io.github.mrmyhuang.cbetar2.metainfo.xml
index 0085603..ec7063c 100644
--- a/buildElectron/io.github.mrmyhuang.cbetar2.metainfo.xml
+++ b/buildElectron/io.github.mrmyhuang.cbetar2.metainfo.xml
@@ -27,6 +27,13 @@
   <content_rating type="oars-1.1"/>
   <releases>
     <release version="20.0.1" date="2022-06-17">
+      <description>
+        <ul>
+          <li>[修正] Electron app 啟動時偶爾讀取離線 DB 失敗。</li>
+        </ul>
+      </description>
+    </release>
+    <release version="20.0.0" date="2022-06-17">
       <description>
         <ul>
           <li>[優化] 升級 Electron 19.0.4.</li>
diff --git a/package.json b/package.json
index 7aca396..63eba07 100644
--- a/package.json
+++ b/package.json
@@ -2,8 +2,8 @@
   "name": "cbetar2",
   "productName": "電子佛典",
   "homepage": "/",
-  "pwaVersion": "9.0.0",
-  "version": "20.0.0",
+  "pwaVersion": "9.0.1",
+  "version": "20.0.1",
   "license": "MIT",
   "keywords": [
     "CBETA",
diff --git a/src/App.tsx b/src/App.tsx
index 506aa25..ef73a80 100644
--- a/src/App.tsx
+++ b/src/App.tsx
@@ -177,11 +177,13 @@ class _AppOrig extends React.Component<AppOrigProps, State> {
     electronBackendApi?.receive("fromMain", (data: any) => {
       switch (data.event) {
         case 'version':
+          // Backend is ready.
           this.props.dispatch({
             type: "TMP_SET_KEY_VAL",
             key: 'mainVersion',
             val: data.version,
           });
+          CbetaOfflineDb.setOfflineFileSystemV2Ready();
           break;
         case 'cbetaOfflineDbMode':
           let dbMode = CbetaDbMode.Online;
diff --git a/src/CbetaOfflineDb.ts b/src/CbetaOfflineDb.ts
index 11328ff..c34f853 100644
--- a/src/CbetaOfflineDb.ts
+++ b/src/CbetaOfflineDb.ts
@@ -75,6 +75,11 @@ async function getFileAsStringFromIndexedDB(file: string) {
     return textDecoder.decode((await IndexedDbFuncs.getZippedFile(file)) as Uint8Array);
 }
 
+let isOfflineFileSystemV2Ready = false;
+export async function setOfflineFileSystemV2Ready() {
+    isOfflineFileSystemV2Ready = true;
+}
+
 export async function init(mode: CbetaDbMode) {
     // Avoid multiple inits.
     if (isInitializing) {
@@ -111,6 +116,15 @@ export async function init(mode: CbetaDbMode) {
             const teiStylesheetString = await getFileAsStringFromIndexedDB(`/${Globals.cbetar2AssetDir}/tei.xsl`);
             await initFromFiles(catalogsString, spinesString, gaijisString, stylesheetString, documentString, teiStylesheetString);
         } else if (mode === CbetaDbMode.OfflineFileSystemV2) {
+            await new Promise<void>(ok => {
+                const timer = setInterval(() => {
+                    if (isOfflineFileSystemV2Ready) {
+                        clearInterval(timer);
+                        ok();
+                    }
+                }, 100);
+            });
+
             const catalogsString = (await readBookcaseFromFileSystem(`CBETA/catalog.txt`));
             const spinesString = (await readBookcaseFromFileSystem(`CBETA/spine.txt`));
             const gaijisString = (await readResourceFromFileSystem(`cbeta_gaiji/cbeta_gaiji.json`));
@@ -363,7 +377,11 @@ async function readResourceFromFileSystem(path: string) {
         electronBackendApi?.receiveOnce('fromMain', (data: any) => {
             switch (data.event) {
                 case 'readResource':
-                    ok(data.data);
+                    if (data.error) {
+                        fail(data.error);
+                    } else {
+                        ok(data.data);
+                    }
                     break;
             }
         });
@@ -376,7 +394,11 @@ async function readBookcaseFromFileSystem(path: string) {
         electronBackendApi?.receiveOnce('fromMain', (data: any) => {
             switch (data.event) {
                 case 'readBookcase':
-                    ok(data.data);
+                    if (data.error) {
+                        fail(data.error);
+                    } else {
+                        ok(data.data);
+                    }
                     break;
             }
         });
@@ -389,7 +411,8 @@ const CbetaOfflineDb = {
     fetchCatalogs,
     fetchAllCatalogs,
     fetchWork,
-    fetchJuan
+    fetchJuan,
+    setOfflineFileSystemV2Ready,
 };
 
 export default CbetaOfflineDb;
\ No newline at end of file
diff --git a/srcElectron/main.ts b/srcElectron/main.ts
index 3d5d334..e4dccb1 100644
--- a/srcElectron/main.ts
+++ b/srcElectron/main.ts
@@ -225,10 +225,21 @@ async function createWindow() {
         mainWindow?.webContents.send('fromMain', { event: 'version', version: PackageInfos.version });
         break;
       case 'readResource':
-        mainWindow?.webContents.send('fromMain', Object.assign({ event: args.event }, { data: fs.readFileSync(`${isDevMode() ? '.' : resourcesPath}/${args.path}`).toString() }));
+        try {
+          const str = fs.readFileSync(`${isDevMode() ? '.' : resourcesPath}/${args.path}`).toString();
+          mainWindow?.webContents.send('fromMain', Object.assign({ event: args.event }, { data: str }));
+        } catch (error) {
+          mainWindow?.webContents.send('fromMain', Object.assign({ event: args.event }, { error: error }));
+        }
         break;
       case 'readBookcase':
-        mainWindow?.webContents.send('fromMain', Object.assign({ event: args.event }, { data: fs.readFileSync(`${settings.cbetaBookcaseDir}/${args.path}`).toString() }));
+        try {
+          const str = fs.readFileSync(`${settings.cbetaBookcaseDir}/${args.path}`).toString();
+          mainWindow?.webContents.send('fromMain', Object.assign({ event: args.event }, { data: str }));
+        } catch (error) {
+          mainWindow?.webContents.send('fromMain', Object.assign({ event: args.event }, { error: error }));
+        }
+
         break;
     }
   });