Sage 50 error: "The header cannot be read from the data source
Sage 50 cannot read the identifying structure at the start of your company data, which points to a damaged, incomplete, or mismatched file.
“The header cannot be read from the data source.”
That message means Sage 50 found your company data but could not make sense of the structure at the front of it. That structure, the header, tells the program what the file is, which release wrote it, and how the records inside are arranged. When the header cannot be read, the file is usually damaged, incomplete, or not what the program expected. Your actual records may still be intact behind it. The same message appears under the Peachtree and Simply Accounting names, which are the US and Canadian names of the same product.
Why does Sage 50 stop at the header?
The header is the first thing the program reads, before any of your transactions or lists. If it is scrambled or missing, the program stops rather than guess at the rest. Three causes cover most cases.
A file gets damaged when a save is interrupted: a power cut, a forced shutdown, or a failing disk partway through a write. A file ends up incomplete when a copy, download, or backup never finishes, so the front of the file is simply not there. Sometimes the file is not what the program expects, because it came from a different edition or release, or because it was renamed into something it is not.
The message also appears during conversions, when a tool reads your Sage data to move it to another program. The reader has hit the same wall: a header it cannot parse. The remedy is the same, which is to sort out the source file first.
Work on a copy first
Before you try anything else, copy the entire company data set somewhere safe and leave the original alone. Repeated attempts to open or repair a damaged file can change it further. Everything that follows should happen on the copy.
Restore from a backup
If you have a backup from before the message started, restoring it is the cleanest way back. Two checks first: the backup must be complete, and it should come from the release you run now. An interrupted backup can carry the same header damage as the live file, so test the restore before you depend on it.
Check the file and the release
If the data was moved or copied recently, the copy may have come up short. Compare its size against the source if you can. Confirm the program is pointed at the real data file, not a shortcut or a partial download. Release matters as well: data written by a newer release generally will not open in an older one. Whether that applies here depends on your file, so treat it as a check rather than a fix.
Files that need professional repair
If no backup restores cleanly and the message persists on a good copy, the header itself is damaged. No setting or reinstall will rebuild it. That is the point where the file needs specialist attention. Our engineers repair damaged Sage 50 and Simply Accounting databases, and every job starts with a free evaluation of the file so you know what is recoverable before committing to anything.
Gather the file as it stands now, every backup you have, and a note of what you were doing when the message first appeared. That is what an engineer needs to judge whether the data can be recovered and what the cleanest route back looks like. Nothing in that first look commits you to a repair.