In all likelihood you have probably just mistakenly switched a setting somewhere to only allow
[IMG2=XXX], I would start checking settings first.
or as a last resort...
...simply recreate the img tags. I've never used vb5 but I presume it has an option to create custom bbcodes like every other version before it:
Example:
Code:
[IMG]picture-url[/IMG]
Replacement:
Code:
<img src ="{param}" alt="img" />