The typical thing to do here is to find out what's actually in the character variable. There is likely something in there that is causing the issue.
Try this:
data have;
input @1 Dosis $8.;
datalines;
155
201
2.1
0.8
123.80
12.0
3333.4
00.6
;;;;
run;
data check;
set have;
put dosis hex32.;
run;
What I get is this:
83 data check;
84 set have;
85 put dosis hex32.;
86 run;
3135352020202020
3230312020202020
322E312020202020
302E382020202020
3132332E38302020
31322E3020202020
333333332E342020
30302E3620202020
NOTE: There were 8 observations read from the data set WORK.HAVE.
NOTE: The data set WORK.CHECK has 8 observations and 1 variables.
NOTE: DATA statement used (Total process time):
real time 0.01 seconds
cpu time 0.01 seconds
All those 2020202020 are spaces, which should be there (all strings are space-padded to full length). Period/Decimal Point is 2E, Digits are 3x where x is the digit (because the ASCII for 0 is 30, not because of any other reason). So for example for the last one, 00.6, 30 means zero, 30 means zero, 2E means period, and 36 means 6.
Check to make sure that you don't have any other characters other than digits (3x) and period (2e) and space (20).
The other thing to verify is that your system is set to use . as the decimal separator and not , as many European systems are - otherwise this requires the commaw. informat. You can actually just try the commaw. informat (comma12. is sufficient if 12 is plenty - and don't include anything after the period) as anything that 12. can read in also can be read in by commaw..