Hi Guys .. I have read some of the responses to this question but still feel problem unanswered (even two computer tech chaps were at a loss)  Spent hours putting together a selection of photos and video clips (from Samsung S6) from a recent charity run ... all seemed well ... saved the project as not yet ready to save the movie ... opened it the following day to see quite a few video clips had been replaced by these yellow triangles .... I closed the programme and reopened ... where there were triangles the video clips appeared but then a different set of clips were affected and replaced by these nasty  triangles  ... every time I closed and reopend the same thing happens ... no sense at all ... I know sometimes if you move a picture etc from the original folder the yellow triangle appears and you can fix it by relocating to the original folder ... this isn't the case with this ... HELP  ... I have lost hours on this an annoying isn't the word ....