"avp14m incorrect length" (often accompanied by similar errors for
) is a classic technical hurdle for users trying to play the arcade version of Alien vs. Predator (1994) via emulators like Why This Happens This isn't a bug in your computer; it’s a version mismatch between your ROM file and your emulator software. ROM Dumps Change
: As emulation technology improves, developers "redump" original arcade chips to get more accurate data. MAME 0.238 Milestone : A significant change occurred in MAME version
. In this version, the expected size of several ROM files—including
—was essentially cut in half to better reflect the actual data on the physical chips. The Conflict
: If you are using a newer version of MAME but an older ROM set (or vice versa), the emulator looks for a specific file size (length). When it finds a file that is too large or too small, it triggers the "incorrect length" error and stops the game from booting. How to Fix It Update Your ROM Set : The most reliable fix is to source an updated
file that matches your current emulator version. If you are using MAME 0.238 or higher, you need the "modern" dump. Match Emulator to ROM
: Alternatively, if you prefer your current ROMs, you can use an older version of the emulator (like MAME 0.200) that expects the older, longer file lengths. Use a ROM Manager : Advanced users often use tools like Clrmamepro
to scan their collections. These tools can sometimes "trim" or fix files to match the expected length for a specific MAME version. RetroArch Specifics : if you are using avp14m incorrect length
The error message "avp.14m - incorrect length" typically occurs when using the MAME arcade emulator to run Capcom’s 1994 beat-em-up classic, Alien vs. Predator. It signals a mismatch between the ROM file size and what the emulator expects for that specific version. What is the "Incorrect Length" Error?
In arcade emulation, every ROM file must have a precise file size (length) and a specific checksum (hash) to be considered valid. If a file is even one byte off, MAME will flag it as having an "incorrect length". The Specific File: avp.14m is a graphics (GFX) ROM.
Common Lengths: Correct versions of this file are typically 1MB (1,048,576 bytes).
The Cause: Older, incorrect "overdumped" versions of these files were often larger, which triggers the error in modern, more accurate versions of MAME. Why This Happens
There are three main reasons you might see this error for avp.14m:
Emulator/Romset Mismatch: Modern MAME is constantly updated for accuracy. A ROM set that worked on an older version (like MAME 0.139) might have incorrect lengths for a newer version (like MAME 0.2xx).
Overdumped ROMs: Early "dumps" of arcade chips sometimes included extra "junk" data at the end. Modern MAME expects "clean" 1MB versions for avp.14m, 16m, 18m, and 20m.
Missing Support Files: Capcom CPS2 games like AvP often require a separate "QSound" BIOS file (e.g., qsound_hle.zip) to function. How to Fix the Error avp14m appears to be a mnemonic identifier —
To resolve the avp.14m incorrect length issue, follow these steps: 1. Audit Your ROMset
The most reliable solution is to ensure your ROM version matches your emulator version.
If you are using the latest version of MAME, you need the latest "Merged" or "Non-Merged" ROM set.
Check the file size of avp.14m. If it is not exactly 1,048,576 bytes, it is likely an outdated version. 2. Check for Parent/Clone Dependencies
The "incorrect length" error for avp14m (typically referring to the ROM file avp_14m.bin within the arcade game Aliens vs. Predator) usually occurs when the ROM file size does not match what your specific version of the MAME (Multiple Arcade Machine Emulator) or FBNeo (FinalBurn Neo) emulator expects. Why this happens
MAME frequently updates its ROM definitions to reflect more accurate "dumps" (copies) of the original game hardware. If you have an older ROM set and try to run it on a newer version of MAME, you may encounter this error because the emulator now expects a different file size.
The MAME 0.238 Change: Specifically, as of MAME version 0.238, the size of four ROMs in the AvP set were cut in half.
Incorrect File Size: The emulator may expect the file to be exactly 1,048,576 bytes (1MB), but your current file might be larger (e.g., 2MB) or smaller. How to fix it Regardless of the exact definition
Update your ROM set: The most reliable solution is to find a version of avp.zip from a ROM set that matches your version of MAME (v0.238 or higher).
Match Core and ROM: If you are using RetroArch, ensure the ROM set version matches the specific MAME core version you have loaded.
Use Clrmamepro: Advanced users can use Clrmamepro to scan their existing ROMs and fix incorrect lengths automatically if the data is valid.
Manual Trimming (Not Recommended): While you can manually trim the file to exactly 1,048,576 bytes using a hex editor, this is prone to error and generally unnecessary if you can simply source the correct ROM.
Check BIOS/Key Files: Some versions of AvP also require specific key files (like avsp.key) or sound files (like qsound_hle.zip) to be present in the same folder.
Are you using a standalone MAME emulator or a frontend like RetroArch?
avp14m appears to be a mnemonic identifier — possibly a:
14m may imply “14 bytes/characters mandatory” or “version 1.4 modified”.Before fixing the error, we must decode the identifier. Based on common engineering patterns, avp14m could be:
Regardless of the exact definition, the error means that whatever process is attempting to read or write to avp14m expected a data chunk of size X, but received a chunk of size Y.
The AVP14M unit is reporting ERR_LEN_MISMATCH when attempting to transmit or write data blocks. The issue manifests under the following conditions: