SQL Server Error 4805 (Severity 17)  typically occurs when there is an issue with data conversion or comparison between columns in a query. Specifically, this error occurs when you attempt to perform operations such as `comparison`, `group by`, or manipulate values of **text**, **ntext**, or **image** data types incorrectly. These three data types are considered deprecated and inherently complex for direct operations because they are designed to store large amounts of unprocessed binary or textual information.  

This error also falls under severity level 17, which indicates that the problem: If migration isn't immediately feasible due to application constraints, explicitly convert your problematic columns may be caused by insufficient system resources (hardware-related issues) or limitations in server design or logic, rather than programming errors.  

Common causes:

• Using functions like `GROUP BY` on columns with these legacy data types (`text`, `ntext`, and `image`). 
• Comparing values from such fields directly using operators (e.g., =, >, <). 
• Incorrect attempts to convert text/ntext/image into another type. 
• Interactions where implicit conversion fails during operations. 
• Attempting arithmetic calculations on text/image-like non-scalar formats.  

To solve this issue effectively: 

1. Inspect Data Types, Check if any column involved in your operation uses the deprecated types: `TEXT`, `NTEXT`, or `IMAGE`.
2. Modify Your Database Design, Avoid using these legacy data types entirely; replace them with modern alternatives (`VARCHAR(MAX)`, `NVARCHAR(MAX)`, etc.).
3. Explicit Conversion Logic, If migration isn't immediately feasible due to application constraints, convert your problematic columns explicitly during querying using functions. 
4. Remove Group By / Comparison Operations Directly on Legacy Columns.