Officerparks24

Beljojo is having server issues.  Have to wait for his server to come back up for his plugins to work. 

Could be a ton of things.
 
Perhaps one of the safe guard checks when it was trying to generate the people related to the callout, discovered that they got created in a building - so it aborts to protect you.
Perhaps it found out that a important person for the situation was for whatever reason, unable to spawn in (maybe your ped pool was full, and it couldn't force another into it because GTA IV limited this.)
Perhaps you are within the minimum distance required to respond to the callout, since moving.  Maybe the minimum was 100, and you where moving towards it when it was sent, and by the time you pressed Y, you ended up being 96 from it, so it aborted..
 
Could be a bunch more stuff - but those seem to be the main ones I'm always seeing. :D

Try to rename the file and remove the .ivaud extension to make it a normal File. Then go into OpenIV, goto the resident.rpf, backup the old WEAPONS file to desktop or specific folder, delete the WEAPONS file in the OpenIV window, drop the new WEAPONS file (the one without the .ivaud extension) into the resident folder in OpenIV, and then click rebuild via the File drop down menu.
 
Hopefully that works, it does for me.

Definitley a Mercedes C-Class if thats the model of your uncle's vehicle. Ladies can't turn that down. Or well, i should say your partner rather. I forgot it's the 21st century. 
 
AND if you can't get ahold of one, then as mentioned above, Crown Vic all the way

Some antivirus programs seem to have issues with the diagnostic tool (and the auto-installer) for no apparent reason. I would recommend adding the diagnostic tool to your antivirus whitelist. Not sure why it would instantly delete a file though, seems a bit weird. Then again, I've never used AVG.