On some computers, LibreOffice Portable 3.5.3 will mistakenly detect that the MS Visual C++ 2008 runtime is not installed when it actually is. We're looking into the exact cause at the moment. If you are affected, you can help us by providing us information on what operating system it's running on and searching your C: drive for the file msvcr90.dll and letting us know where it is installed. We already have a partial fix working, but this could help provide us with a complete one encompassing any edge cases.
Fix 2: Better detection
First, please try LibreOfficePortable.exe launcher fix 2. Download and replace your current launcher in the LibreOfficePortable directory. It has correct detection of an installed VC runtimes.
Workaround: Patched Launcher
After that, if you'd like to turn off the message, just download this this patched LibreOfficePortable.exe launcher. You can replace the existing one in your LibreOfficePortable directory. This patched launcher has VC runtime detection disabled so you don't have to worry about the message appearing every time you run it.
We'll have a fixed version up in the next few days. Thanks for your patience.