Fix Error 20599 “Cannot Open SQL Server” in VB6 / Crystal Reports Applications – Complete Troubleshooting Guide

The error “Error Number: 20599 – Cannot open SQL server” is a common issue in legacy business applications built using VB6, ODBC, and Crystal Reports. This error typically occurs when the application fails to establish a connection with the SQL Server database.

It is especially common in environments where:

• Multiple SQL Server instances are installed
• Systems are migrated (physical → cloud server)
• ODBC / DSN configurations are outdated
• Crystal Reports runtime dependencies are mismatched

This article provides a step-by-step technical approach to identify and fix the issue effectively.

⚠️ Error Description

Error Message:

Error Number: 20599  
Error Description: Cannot open SQL server  
Module: JobRouteCard  
Procedure: tbMenu_ButtonClick

? Meaning:

The application attempted to:

• Connect to SQL Server
• Fetch data (often for reports)

But failed due to:

• Incorrect connection settings
• Database unavailability
• Authentication or network issues

? Root Causes

1. SQL Server Instance Mismatch

Systems with multiple instances like:

• MSSQLSERVER (Default)
• SQLEXPRESS
• SQLEXPRESS01

The application may be pointing to the wrong instance.

2. SQL Server Service Issues

If SQL services are:

• Stopped
• Hung
• Misconfigured

Connection will fail.

3. ODBC / DSN Misconfiguration

Legacy applications depend on:

• 32-bit ODBC Data Sources

Incorrect DSN settings lead to connection failure.

4. Database Not Attached or Missing

After migration:

• Database may not be attached
• MDF/LDF files may be missing

5. Authentication Failure

• Invalid SQL username/password
• SQL Authentication disabled
• Permission issues

6. Network / Firewall Restrictions

When SQL is hosted on another machine:

• Port 1433 blocked
• SQL Browser disabled
• Server not reachable

7. Crystal Reports Runtime Issues

If the error occurs while opening reports:

• Missing runtime
• Version mismatch (CR 8.5 vs newer runtime)

? Step-by-Step Troubleshooting

✅ Step 1: Verify SQL Services

1. Open services.msc
2. Ensure:
   • SQL Server (MSSQLSERVER) → Running
   • SQL Server (SQLEXPRESS) → Running
   • SQL Server Browser → Running

✅ Step 2: Identify Correct SQL Instance

Open SQL Server Management Studio (SSMS) and test:

localhost
.\SQLEXPRESS
.\SQLEXPRESS01
SERVERNAME
SERVERNAME\SQLEXPRESS

✔ Use the instance that connects successfully

✅ Step 3: Verify Database Availability

In SSMS:

• Expand Databases
• Confirm:
  • Database exists
  • Database is online

If missing:

Right Click → Attach Database

✅ Step 4: Check Authentication

Try both:

• Windows Authentication
• SQL Server Authentication

Ensure:

• Login exists
• Password correct
• User mapped to database

✅ Step 5: Verify ODBC Configuration

Open 32-bit ODBC:

C:\Windows\SysWOW64\odbcad32.exe

Check:

• System DSN
• Correct server name
• Database selected

✔ Click Test Connection

✅ Step 6: Validate Network Connectivity

If using remote SQL Server:

ping SERVERNAME

Test using IP:

192.168.1.10\SQLEXPRESS

Also ensure:

• Port 1433 open
• Firewall allows SQL

✅ Step 7: Check Crystal Reports Runtime

If error occurs on report click:

• Install correct runtime version
• Ensure compatibility with application
• Reconfigure report datasource

? Special Case: Server Migration (Physical → Cloud)

Common issues after migration:

• Old server name still used
• DSN not updated
• Database path changed
• SQL instance renamed

✔ Solution:

• Update connection string
• Recreate ODBC DSN
• Verify database attach

⚡ Quick Fix Checklist

✔ SQL Server running
✔ Correct instance used
✔ Database attached
✔ Login working
✔ ODBC DSN correct
✔ Network accessible
✔ Crystal runtime installed

? Conclusion

Error 20599 – Cannot open SQL server is not a software bug but a configuration issue. It typically arises due to mismatched SQL instance names, incorrect ODBC settings, or database connectivity failures.

By systematically verifying:

• SQL services
• Instance name
• Authentication
• ODBC configuration

You can resolve the issue quickly and restore application functionality.