Facing issue in loading Report which contains Main and Sub report using Report builder in SSRS

Based on the error in the SSRS log and the fact that the same RDL works in Production but times out in QA, focus on SSRS-side processing rather than the database engine:

1. Check for rsProcessingError details
   • In the SSRS log, search for ReportProcessingException and the specific error text about "no data for the field at the position 16".
   • This typically indicates a data/field mismatch during report processing (for example, a field index or name expected by the report does not exist in the dataset returned in QA).
   • Use the full error text and stack trace in the log to identify which dataset and which report item (textbox, tablix, etc.) is failing.
   • For more guidance, see the rsProcessingError troubleshooting steps: view the full error text, use the Error List in Report Designer/Report Builder, and check the server logs for ReportProcessingException.
2. Verify dataset schema vs. report definition in QA
   • Confirm that the stored procedure or query in QA returns exactly the same columns (names, order, and data types) as in Production.
   • The error mentioning a field at a specific position (e.g., 16) suggests the report expects a field that is missing or has changed position in the QA dataset.
   • Compare the RDL’s dataset field definitions with the actual result set in QA. If the QA database has different schema (extra/removed/renamed columns) or different result shape due to environment-specific data, align it with Production or update the report definition.
3. Check subreport compatibility and versioning
   • When a main report uses subreports, the same version of the Reporting Services report processor must process all of them. If QA has a different SSRS version or if only some reports were upgraded, subreports can fail with processing errors.
   • Ensure the main report and all subreports in QA are deployed from the same RDL sources and are compatible with the SSRS version in QA.
   • If any report failed to upgrade, re-deploy or upgrade it so that the same report processor version handles both main and subreports.
4. Validate expressions and field references
   • In both main and subreports, check expressions that reference dataset fields:
     • Make sure field names exist in the dataset and are spelled correctly.
     • Ensure filters and expressions do not reference fields that have errors or are missing.
     • Verify that filter expressions and filter values use matching data types; mismatched types can cause processing errors.
5. Compare parameters and subreport parameter mapping
   • Ensure parameter definitions (names, data types, multi-value vs single, nullability) are identical between environments.
   • Verify that the main report passes parameters to the subreport correctly and that the subreport’s datasets handle those parameters without returning a different schema or error in QA.
6. Reproduce and isolate
   • Run the subreport directly in QA with the same parameter values used by the main report to confirm it renders successfully and returns the expected fields.
   • If the subreport runs but the main report fails, focus on the parameter mapping and any expressions in the main report that reference subreport-related datasets.
7. Use SSRS logs for deeper diagnosis
   • As recommended for rsProcessingError, use the SSRS log file on the QA server to get the exact dataset and field causing the error. The log path is typically similar to:
     • <drive>:\Program Files\Microsoft SQL Server\<Instance>\Reporting Services\LogFiles\ReportServerService_*.log.
   • Once the failing field/dataset is identified, adjust the QA database schema, stored procedure, or RDL dataset definition accordingly.

After aligning the dataset schema, field references, and ensuring the same report processor version and subreport definitions in QA, the timeout should disappear because the report will no longer be stuck in repeated processing failures.

References:

• rsProcessingError - Reporting Services error
• Troubleshoot subreports in Power BI paginated reports
• Reporting Services log files and sources
• Subreports in SSRS not working