QB Issue Resolution:
As of April 2017, the ability to upload BMP files was already removed. This is due to the security risks it creates when it is uploaded to QuickBooks Online (QBO). For this reason, I would suggest that you convert your file to JPEG or PNG before you upload it to QBO. Please consult an IT Professional or an expert in your company when you do it.
If you have used this type of file before, please download and convert them to JPEG or PNG. Then, re-attach them to your transactions. I know this is easier said than done, but please consider this as a way to protect your files from malware or viruses.
These are the updated list of supported file types for attachments: PDF, JPEG, PNG, DOC, XLS, CSV, TIFF, GIF, and XML.
Resolution for Issue 'Why will it no longer allow me to attach a .BMP file? Used to work just fine but now it wont.' available: Yes (Solved).
Source: Intuit Community forum.
Why will it no longer allow me to attach a .BMP file? Used to work just fine but now it wont.: this issue or error code is a known issue in Quickbooks Online (QBO) and/or Quickbooks. Support for this issue is available either by self-service or paid support options. Experts are available to resolve your Quickbooks issue to ensure minimal downtime and continue running your business. First try to resolve the issue yourself by looking for a resolution described below. If it is a complex issue or you are unable to solve the issue, you may contact us by clicking here or by using other support options.Support for BMP file
Quickbooks Repair Pro will resolve it efficiently and affordably. Guaranteed resolution of your issue, or you pay nothing!
Error Recovery for BMP file [Canada]
E-Tech is the #1 Quickbooks data migration and Conversion service provider.
Additional Support Options: