The quick fix:
- Chech fpc, (below),
then
- Menu "Tools" > Configure build Lazarus >
there is a radio "Clean all, select it
then build
- Also to be save. Menu "Tools" > Rescan fpc sources
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To know more about the error: on the messages window, right click, "copy all and hidden"
There are additional hints usually.
But it may be a problem with the upgrading.
A possible guess: You still use an old FPC, if you used an old fpc before, and did not "uninstall" during the new install, then you have 2 fpc installed.
The installer does not touch your config, so it still points to the old.
-----Check fpc:
Menu Tools > options
All entries (fpc, fpc sources, make) should contain 2.6.2
C:\lazarus\fpc\2.6.2\ .....